MYCOLOGIA OFFICIAL ORGAN OF THE MYCOLOGICAL SOCIETY OF AMERICA

VOL. LXIV JANUARY-FEBRUARY, 1972 No. 1

EVOLUTION OF THE FUNGI'

ROY F. CAIN

Department of Botany, University of Toronto, Toronto, Ontario, Canada

I am very grateful to the members of the Mycological Society of America for the privilege and honor of serving as President as well as for the opportunity of presenting this address.

I do not propose to review the numerous theories dealing with the phylogeny of the fungi published by various mycologists. The diversity of these views and the failure of any of them to receive wide acceptance indicates that they are not very accurate. I intend merely to outline my own views as to the origin and evolution of the Ascomycota and Basidiomycota thus adding one more fantastic scheme to the already existing ones.

My approach to the subject is completely different to that published previously. I believe that nothing is gained by any sort of phylogenetic tree obtained by an arrangement of present-day genera, families, orders, etc. The origin of the Ascomycota is so ancient that it is very unlikely that any of the early genera would have survived into the present. Probably in the early stages of evolution the species were less adapted to their environment than present-day ones, consequently they were eliminated in competition by their better-adapted descendants.

When thinking of relationships, mycologists have been strongly influenced by the dichotomous keys so universally used in identification

1 Presidential address, Mycological Society of America, Bloomington, Indiana, August 25, 1970.

[MYCOLOGIA for November-December, 1971 (63: 1099-1284, i-viii was issued January 12, 1972]

The New York Botanical Garden 1972.

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ROY F. CAIN PRESIDENT, MYCOLOGICAL SOCIETY OF AMERICA, 1970

MYCOLOGIA, VOL. 64, 1972

of fungi. In this system single characteristics are taken up in sequence, one at a time, leading one to think of relationships based on single features.

In the extensive and very useful classification proposed by Winter (1884-1887), the depth of the ascocarps in the substrate played an important part. This feature has been found to be less and less reliable as an indicator of relationship. In the same publication, the presence or absence of hairs on the ascocarp was significant in family delimitation. In many cases, this feature is now regarded as of little value even at the generic level. Likewise Winter placed considerable emphasis on the extent of the stroma. In some species of Hypocopra, an extensive stroma completely surrounds the perithecium except for the ostiole, while in others, the stroma is reduced to a thin, felt-like layer of hyphae on the surface of the substrate. Single characters are useful in keys but in most cases they are very unreliable in determining relationships.

Most features found in the Ascomycota and to some extent in the Basidiomycota (excluding such complex features as the spore discharge mechanisms) have appeared separately in two or more lines. It is rela- tively easy to find characters which appear to be connecting links be- tween various taxa at almost any level including genera, families and orders. Unfortunately, when all these connections are put together you find that any particular taxon can be linked in t11 directions rather than in an orderly ascending phylogenetic tree.

An almost infinite number of such trees can be constructed depending on the features chosen at any particular level. Permit me to cite an extreme case in which the effect of KOH on the cell wall has been studied. In Tubulicrinis (Corticiaceae) the wall of the cystidium is quickly dissolved. Similarly, in Lasiosphaeria strigosa (Alb. & Schw.) Sacc. (Sordariaceae), the wall of the hairs on the ascocarps are also dissolved in KOH. However, this is clearly not an indication of relationship between the two. In Kernia there are long dark hairs on the ascocarp which are considered characteristic for the genus. In our laboratory we have encountered one species without these hairs but possessing the other features typical of the genus. This species is being published in Kernia rather than in a separate genus based on a single character.

One must always evaluate the presence or absence of a single feature in the light of all available evidence. As illustrative of this, one might cite the reaction of hyphae and spores to Melzer's reagent. Sometimes the technique appears useful only at the species level, as in Amanita; at other times it is effective at the generic level (Gloeocystidiellum)

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CAIN: EVOLUTION OF THE FUNGI

(Corticiaceae) while in still other instances, the feature can be significant as a family characteristic (Russulaceae and Stereaceae).

Rather than relying on a single feature in determining relationship, it is better to take into consideration all characteristics of a group of species when deciding whether they are congeneric. A complete generic description can then be made, though it is still quite possible that none of the included species will possess all of the generic characters. Each species may lack one or more of the features and it may become in- creasingly impossible to find any single criterion which can be used to key out a genus in such a way as to include all species belonging to it, without incorporating the species several places in the key. As a result, if a chart is constructed of any group of taxa, such as species of a genus together with their characteristic features, the result is a checkerboard system of arrangement rather than a dichotomous one.

Therefore, the only conclusion possible is that a repetition of the same feature has appeared in a number of different lines of evolution. Numerous examples of the duplication of features as an adaptation to a particular environmental niche by different lines in the evolution of the fungi can be cited; among these is the similarity in the fruit bodies of the Tuberales and underground Gastromycetes.

This duplicity frequently results in convergence as is demonstrated in species that have been assigned to the Plectascales, Perisporiales, Erysiphales and Tuberales. Members of these orders and the Gastro- mycetes, have adopted a mode of spore dispersal by animals of various kinds, or, if dispersal is aerial, then there is a delay until sometime after maturity of the fruit body. The latter type of dispersal is also character- istic of the Myxophyta.

Over a period of years I, and more recently one of my students, Mr. David Malloch, have been investigating saprophytic cleistothecial species of fungi. In his recent thesis, Malloch (1970b) has included only species with a distinctly closed peridium around the ascocarp, therefore the Gymnoascaceae have been excluded. He has recorded 262 species. They are distributed in 73 genera and 18 families. A few genera cannot be placed in families because of inadequate data.

Of the 18 families included, only seven are exclusively cleistothecial. With the exception of the Onygenaceae and Monascaceae whose affin- ity is with the Pezizales, the families are related to various orders of ostiolate Ascomycota. One new family and probably Zopfiaceae belong in the Loculoascomycetes. The Eurotiaceae is clearly derived from the Hypocreales; the separation is sufficiently distinct to warrant using this family name for the cleistothecial species. The remaining 11 families

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MYCOLOGIA, VOL. 64, 1972

are predominantly ostiolate but some cleistothecial genera are included as well. In all cases, the relationship between the genera with the two types of ascocarps is so close that family separation is unjustified; otherwise it would necessitate creating 11 new families.

In order to conform with the concept of separating the nonostiolate Plectascales from the ostiolate orders, several years ago I established two new families, Tripterosporaceae (Cain, 1956b) and Phaeotrichaceae (Cain, 1956a). When I realized the close affinities involved and the large number of new families which would result, the idea was relin- quished; however, Phaeotrichaceae is still a good family since the ostiolate genus Trichodelitschia has no other family affinities. On the other hand, Tripterosporaceae should be included in the Sordariaceae.

A number of genera included in the Thelebolaceae have given rise to cleistothecial species with the apothecia remaining permanently closed until after the deliquescence of the asci. The Erysiphales apparently had their origin amongst the Pezizales at a time when members of the order (Pezizales) were in an early stage of evolution.

The highly specialized cleistothecial line has become sufficiently separated to warrant maintaining at least a family for them. Here I might point out a few relevant facts. There are very few, if any, leaf parasites among the Pezizales. There are very few saprophytic cleisto- thecial genera in the Loculoascomycetes and none are recognized as having come from the Inoperculate Discomycetes. It is my belief that Helicogonium (White, 1942), Myriogonium (Cain, 1948) and pos- sibly the Taphrinales, which lack ascocarps, have evolved from the latter.

While the Inoperculate Discomycetes have produced no cleistothecial forms, at least one genus (Roesleria) has evolved from them. The asci are evanescent and produce a powdery mass of ascospores on the surface of a dry globose head which is raised on a stalk.

The situation in the Erysiphales is somewhat special. The species are successful leaf parasites despite the absence of spermatia. This ob- servation necessitates elaboration. The mycelium is superficial on the leaf surface rather than internal as in most leaf parasites. Conidia are produced profusely throughout the growing season so that there is ample opportunity for multispore colonization of single leaves. Plasmog- amy is readily accomplished between colonies of different genetic types by means of fusions between ascogonia and hyphae containing the appropriate types of nuclei. The terlr antheridia has not been used for cells fusing witli the ascogonia since I do not believe its use is justifiable in any of the Ascomycota.

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CAIN: EVOLUTION OF THE FUNG;I

The cleistothecial Plectascales catnot meet the requirements of an ancestral line for all or any of the Ascomycota with apothecia or with ostiolate perithecia for two reasons, firstly, they are too highly special- ized, secondly, the links between the two groups are at too many points. For example, in the case of the ascus, one anticipated requirement would be numerous repetitions of the evolution of its complicated apical struc- ture. It would be unreasonable to expect that such complicated struc- tures could have evolved separately in so many different lines.

Another point in question is the designation cleistothecium. This term has lost most of its previous significance since some of us today maintain that it represents either an apothecium or an ostiolate peri- thecium which has failed to develop an aperture for the forcible dis- charge of the ascospores.

While on the subject of ascocarps I would like to discuss some in- consistencies in the use of the terms pseudothecium and pseudoparaph- ysis. If pseudothecium is to be applied to the ascocarps of all Loculo- ascomycetes then it should be used for the apothecia of the Patellariaceae as well as the fruit bodies of many of the lichenized Ascomycota, both of which belong in the Loculoascomycetes. If pseudoparaphyses are to be defined as growing downward then the term pseudothecium should be considered applicable to the ascocarps of the Hypocreales. However, these sterile filaments do not always grow downward, for example in the apothecia of the Patellariaceae, and in some other genera they grow inward from all sides of the ascocarps.

If the term pseudothecium is to be applied to all ascocarps whose initial development takes place prior to the appearance of the ascogonia or entirely without them, then it should also be applied to the fruit bodies of Inoperculate Discomycetes and such genera as Morchella, Helvella and Geoglossum. In all of these, the ascocarps are as stromatic as those in the Loculoascomycetes and the terms pseudothecia and pseudoparaphyses should be used. The distinction between stromatic and nonstromatic tissue when applied to ascocarps has little or no real significance.

In addition, there are probably many other species distributed through many taxa of the Ascomycota in which the ascogonium, though present, may have no significant function in the sexual process. In these species, plasmogamy is probably accomplished by hyphal fusion as in the Hymenomycetes. The dikaryon may be maintained in the my- celium despite the absence of clamps on the hyphae. All tissues in the ascocarp may be dikaryotic even though individual cells may be uni- nucleate. Fusion between uninucleate cells in the paraphyses of some

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ascocarps (particularly Phacidiales) as well as fusion between the ascogonium and an adjoining filament from the same hypha (as in Monascus) may have some significance in reestablishing the dikaryotic cell which becomes the ascogenous system with croziers. In my opinion, the possibility of plasmogamy occurring by hyphal fusion in the Ascomy- cota has been greatly neglected. If plasmogamy takes place on the hyphae in members of the Loculoascomycetes, the ascogonia may have been lost since they are not essential for ascocarp initiation. In the majority of the other groups of Ascomycota (except Inoperculate Discomycetes) the ascogonium is retained, its sole function being that of initiating ascocarp production.

In the absence of any significant fossil record it is necessary to rely on the application of general phylogenetic principles, as adequately enumerated by Savile (1955). The few fossils that have been found appear to be essentially similar to present day Ascomycota and Basidio- mycota. At this point, I would like to interject a few comments with regard to the origin of parasitic fungi. They represent highly specialized organisms. The difficulty which one experiences in attempts made to culture them and the tendency of these fungi to produce fruit bodies less readily than the corresponding saprophytes are indications of this high degree of specialization. The host specificity is further evidence of their specilization. I cannot agree that any major group of fungi could have had their origin in parasitic lines.

I can see no justifiable way in which any of the Phycomycota could have evolved into the Ascomycota. The two divisions are so funda- mentally different in their morphology, developmental pattern and sexual mechanisms that any direct connection is ruled out. A number of lines of the Phycomycota have very successfully adapted themselves to a terrestrial habitat. Some of the Phycomycota even exhibit forcible sporangium or spore discharge as in Pilobolus, Entomophthora and Conidiobolus, however, none of these resemble any Ascomycota. I would completely reject the concept of the Phycomycota as the origin for either the Ascomycota or the Basidiomycota.

The ancestral species or group of species must have been highly un- specialized and must have possessed considerable genetic plasticity be- cause of the great diversity among the Ascomycota especially the lichen- ized ones. Rather than looking among the existing species of fungi, it appears to be more profitable to examine all of the various Ascomycota and predict what sort of species would most likely be the source of such an extensive division.

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CAIN: EVOLUTION OF THE FUNGI

It is essential to provide for a gradual and orderly evolution. The heterotrophic fungi are too highly specialized to qualify as an ancestral line. I believe that the ascus with its unique mechanisms for the aerial dispersal of ascospores originated on autotrophic plants at a time when they moved from sea to land. The basically different types of asci had their origin at this stage.

In all the ancestral lines, the plants were autotrophic with a discrete haploid thallus. A dikaryotic stage was always parasitic on it. Each plant produced both ascogonia and spermatia on unique phialides. Cross fertilization was assured by having two mating types which were mor- phologically indistinguishable. As these plants became adapted to the land habitat, they evolved into a flora of great complexity both as to the number of taxa and as to their considerable diversity in morphological structure. Since their existence is only hypothetical, it is impossible to give them a scientific name. However, in order to refer to them I propose using the name ascophytes.

The autotrophic ascophytes evolved on soil in a tropical, moist climate, sites which are now occupied by complex rain forests. All evidence indicates that this evolution took place at an early geological period before the origin of vascular plants, and perhaps, even before the origin of Chlorophyta. The ascophytes, with their comparatively simple structure, were able to occupy such sites due to lack of com- petition with larger vascular plants.

These autotrophic ascophytes resembled in form and structure the present-day lichenized Ascomycota except for the lack of xerophytic modifications and except for the absence of the algal component. The thalli evolved into a great diversity of foliose and fruticose types con- sisting either of hyphae or pseudoparenchyma, or a combination of both. They produced ascocarps in or on the thalli with ascospores which were forcibly discharged into the air.

As with most communities, some species adapted themselves to a parasitic existence. This resulted in the origin of the lichen parasites- the first heterotrophic Ascomycota. In such a favourable environment there was a great profusion of epiphytes including the Cyanophyta and evenutally the Chlorophyta. These filamentous and unicellular algae became so abundant that they seriously shaded the thalli of the asco- phytes, which, eventually, were forced to utilize the carbohydrates of the algal cells with which they were in contact. This resulted in a gradual diminution and final disappearance of the chlorophyll of these plants. The ascophytes probably lacked chlorophyll B and hence may have been less efficient than the Chlorophyta.

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MYCOLOGIA, VOL. 64, 1972

The autotrophic ascophytes thus evolved into the heterotrophic lichenized Ascomycota and gradually incorporated the epiphytic algae into their loose thallus structure. The protective cortical tissue of pres- ent-day lichenized Ascomycota was a later development which was evolved as an adaptation to colonization of a progressively more and more xerophytic habitat.

The appearance of larger vascular plants had two major effects. First, it provided larger masses of plant tissue as a substrate for other plants. It is possible that some of the surviving autotrophic ascophytes developed as epiphytes on these larger vascular plants. They may then have gradually become parasitic and heterotrophic by the loss of their own chlorophyll. Others may have become saprophytic heterotrophs directly by colonizing dead parts of tile vascular plants. The second effect was the direct competition of the autotrophic ascophytes and the new vascular plant flora. These larger vascular plants subsequently succeeded in completely eliminating the smaller, free-living ascophytes. The lichenized Ascomycota have survived only on xerophytic sites or on those areas otherwise unsuitable for the vascular plants. The auto- trophic ascophytes living on soil probably had hyphal or rhizoidal attach- ments to the substrate.

In heterotrophic Ascomycota (except in the lichenized species) there has been a gradual diminution and eventual loss of the thallus. Two examples of it exist, for example, the stroma of the Diaporthaceae and Xylariaceae and the tissue giving rise to the ascocarps such as in the ascocarp primordium of the Inoperculate Discomycetes.

The Operculate Discomycetes are rather unique among the Ascomy- cota. Probably they have evolved from a special group of autotrophic ascophytes which separated at an early stage from the ancestrial line and evolved a unique apical structure in the ascus as it adapted to the terrestrial habitat. It is noteworthy that, to my knowledge, there are no operculate representatives among the lichenized Ascomycota. Per- haps there was something about the structure of the ancestral line which was different from those lines giving rise to the lichenized Asco- mycota and which was unsuitable for lichenization. In order to sup- port this contention I would say that there probably were no spermatia present in that line giving rise to the Operculate Discomycetes; although these were evidently present in all the other major groups of the Ascomycota except the Xylariaceae.

In all lines of evolution in the Ascomycota and Basidiomycota, spermatia were small, hyaline, ovate cells produced on phialides. In the Loculoascomycetes they were typically produced in spermagonia,

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CAIN: EOVOLUTION OF THE FUNGI

while in the Inoperculate Discomycetes they were borne in acervulus- like structures. In the majority of the other Pyrenomycetes the phialides were scattered on the hyphae. In many lines of the Ascomycota spermatia have taken over the function of vegetative reproduction, and in so doing have been gradually modified. These modifications are as follows: a change from wet to dry spores, increase in size, elongation, formation of septa and pigmentation. With these changes there have been modi- fications in the phialides involving elongation, pigmentation and the production of rings at the apex forming annellophores. There has also been a gradual increase in the distinctiveness and complexity of the phialophores. They have become more elongated and upright as an adaptation to aerial dispersal of the conidia. Conidia produced in acervuli and pycnidia have retained their primitive wetness. The extent to which these changes have progressed is one of the most reliable means of assessing the degree of evolution of a taxon. In this respect the Hypocreales to which the Eurotiaceae should be assigned are the most highly evolved. It is significant that there probably are no lichenized Hypocreales and of course no lichenized Eurotiaceae. In contrast to this there are many plant parasites of various types in the order. In the Microascaceae (Malloch, 1970a) there has been a further evolution of the phialide into an annellophore with the imperfect state classified as a Scopulariopsis or Doratomyces. In the latter, the annellophores are grouped in synnemata.

The failure of the Pezizales in establishing themselves as leaf para- sites may be due to the fact that they lack spermatia. No spermatia or conidia produced on either phialides or annellophores have ever been reported for any of the Pezizales. If any of these spore types were ever produced by members of this order or the immediate ancestor, they must have disappeared very early in the evolution.

The absence of lichenized Pezizales may be due to their having had the evolution of the ancestral line after the period during which the lichens originated. However, the origin of the order must have been sufficiently ancient to allow for the considerable diversity of the pres- ent-day species. In addition, it has been the source of the cleistothecial families Monascaceae, Onygenaceae, Gymnoascaceae and Erysiphaceae. All of the families agree in the complete absence of phialides and annellophores.

The yeast have evolved, probably in several lines, as an adaptation to growth in a liquid medium, utilizing the sugars. Typical habitats are the exudates of woody plants, and the juicy fruits and nectaries of flowers on Angiosperms. Thus they are end lines that have evolved

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AMl YCOLOGIA. VOL. 64. 1972

along with the Gymnosperms and Angiosperms, in a comparatively recent period, adapting themselves to the environment by a loss of the ascocarps. In most of the yeasts, hyphae have been replaced by budding cells or blastospores. Hansenula, commonly found in the logs of conifers on the surface of the wood beneath the loosened bark, is probably de- rived from one of the sections of Ceratocystis.

Cephaloascus (Hanawa, 1920; Wells, 1954) is likewise a special reduced end line, derived from Ceratocystis, in which the ascocarp has been lost and the asci develop in chains at the apex of a filament re- sembling, and probably derived from, a conidiophore.

In both genera there is a similarity in habitat, an association with insects and the same type of ascospore, hemispherical with a brim- like sheath.

The Basidiomycota are basically so different from the Ascomycota in their morphology, life cycle, and means of spore ejection, that there is no logical method of either one evolving from the other. For this reason, I prefer to separate them in different plant divisions. The mechanism involved in the discharge of the basidiospores is quite un- related to that of the ascospores. Both are highly successful and accom- plish the same thing-that is. getting the spores into the air currents. It is difficult to visualize a simple mutation which would change an ascus into a basidium. Any intermediate type involved in a gradual change would be so inefficient as compared to the parent that it would be eliminated by competition.

The metabasidium is not actually comparable to the ascus. The ascus has evolved from a sporangium developed by the dikaryon as a means of producing disseminating bodies. On the other hand, the meta- basidium has been derived from a haplont plant produced by a dikaryotic plant. The haplont is always parasitic on the dicaryon. Then, it is this haplont plant which produces the disseminating bodies. In the Basidio- mycota the haplont plant has been finally reduced to the single-celled basidium with its basidiospores, while in the Ascomycota, it is the haplont which is the independent dominant part of the life cycle. Only in a few evolutionary end lines such as some of the Geoglossaceae, Helvellaceae and Morchellaceae has the dikaryon become free from being parasitic on the haplont.

As in the Ascomycota, so in the Basidiomycota, the evolution of basidiospore discharge mechanism took place during the period when the ancestral line was still autotrophic and as it became adapted to land habitats rather than marine. The autotrophic ancestors of the Basidio- mycota I will refer to as basidiophytes.

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CAIN: EVOLUTION OF THE FUNGI

Such autotrophic basidiophytes probably had a life cycle similar to that of the Uredinales which I regard as having the most primitive life cycle among the Basidiomycota. In this type of life cycle both haplont and the dikaryon had an independent, free-living generation. In the ancestral line, both of these generations produced their own chlorophyll, and possibly in one or both generations, the thalli were formed of loose, hyphal-like filaments rather than the solid thallus of the ascophytes. In the autotrophic basidiophytes the free-living haplont produced a di- karyotic structure as a parasite on it, whose main or sole function was to produce disseminating spores. In the Uredinales this structure has become the aecium, so, evidently, it is the aecium not the basidium or basidiocarp which corresponds to the ascocarp in the life cycle.

In the basidiophytes the dikaryotic spores produced an independent dikaryon which was repeated by the production of dikaryotic spores. Eventually, in certain independent and separate cells of the dikaryon, the two nuclei fused and underwent meiotic division. Each of these cells then grew out to produce a haplont filament with uninucleate cells and parasitic on the dikaryon. This haplont plant then produced disseminat- ing spores one on each cell which, on germination, produced the separate haplont generation. It was the cells of the parasitic haplont which evolved the shooting mechanism so characteristic of the Basidio- mycota as they adapted to a terrestrial instead of a marine habitat. Whatever the size may have been in the autotrophic plants it has been limited or reduced to four cells in present-day heterotrophic Basidio- mycota.

In the Class Hymenomycetes this haploid plant has been further reduced to one cell by elimating the septa but it is still a parasite on the dikaryon and its sole function is dissemination by producing the basidiospores. The basidiospores are thus the disseminating bodies of parasitic haploid plants whereas ascospores are the corresponding dis- seminating bodies of parasitic dikaryotic plants. If the basidiophytes migrated to the land during the same period as that of the ascophyte migration, then, they must have had a different structure and did not form the dominant part of the vegetation. Neither did they become lichenized during the period of ascophyte lichenization.

There is also the possibility that the basidiophyte evolution took place during a period later than that of the ascophytes. The few pres- ent-day Basidiomycota lichens merely have algal cells associated with highly evolved basidocarps of clavarioid or thelephoroid fungi. The evolution of the heterotrophic Basidiomycota took place much later than the lichenization of the Ascomycota which, as I indicated previously,

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MYCOLOGIA, Vo-,. 64, 1972

preceded the evolution of the vascular plants. Probably, it took place during the early period of vascular plant evolution.

The appearance of heterotrophic Uredinales was contemporary with the ferns and gymnosperms. In the forest of vascular plants which re- placed the ascophytes there were the epiphytes as usual. Among these epiphytes were the autotrophic basidiophytes, the haploid as well as the independent dicaryotic plants. It was a simple step for an epiphyte on the leaf or frond of a vascular plant to extend the anchoring fila- ments into the stomata or eventually through the surface layer of cells. Once inside they began absorbing the nutrients of the cells with which they came in contact. With such a convenient source for all their requirements they gradually lost their chlorophyll and became completely heterotrophic. Eventually, the complete development took place inside the leaf tissue of the host with the fungus breaking to the surface to produce the disseminating spores.

This evolutionary process was completed for each of the two inde- pendent generations but on different hosts. It may even have been re- peated in more than one species. The dikaryon must have been on a fern or its ancestor. The haplont was on a gymnosperm or its ancestor which must have given rise to both monocotyledons and dicotyledons provided the rust line goes back to a single species.

The parasitic Uredinales have continued to evolve with their hosts, and gradually diverged into the various lines of host plants. I can see no reason to believe that any rust fungus has ever jumped from one host to another. In order to explain some of the peculiar host-parasite re- lationships it may be necessary to conclude that the parasitic habit de- veloped independently in more than one species.

Among the Basidiomycota only the Uredinales have retained the sexual structures-the male spermatia produced on phialides and the female aecial primordium. If this female structure is typical of that in the autotrophic basidiophytes, then it is completely different from the ascogonium in the ascophytes. The spermagonium of the Uredinales with its phialides and spermatia is so similar to that in the Ascomycota that they have been described as species of imperfects in genera such as Perisporium. This, together with the production of a dikaryon in both divisions, leads to the conclusion that the Ascomycota and the Basidiomycota may have had a common ancestor. However, the dif- ferences between the two divisions are so extensive that the diversion must have taken place very early in the evolution of the autotrophic ascophytes and basidiophytes.

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CAIN: EVOLUTION OF THE FUNGI

The similarities between these two divisions and the Rhodophyta leads to the conclusion that it too must have been included in the com- mon ancestry. However, that line has also diverged at a similar very early period.

Thoughout the evolution of the Uredinales there has been a con- tinued tendency toward simplification, for example, the elimination of various stages to the point when in one of the simplest types the metabasidium or haplont is produced directly on the aeciospore, only, finally to be replaced by the production of a hypha.

There has been considerable modification in the nuclear cycle and heteroecism has frequently been replaced by the autoecious habit. Re- tention of the spermagonia in the heterothallic rusts can be easily ex- plained. The haploid plants usually occur as monospore colonies on separate leaves. The effect is the same as having individual thalli such as the gametophytes of ferns which are separated in space. Spermatia are essential for cross fertilization from leaf to leaf.

Throughout the Hymenomycetes there has been very considerable reduction and modification from the ancestral line. They have become adapted to the utilization of large masses of substrate provided by vas- cular plants. Most of them live in the soil, on the surface or roots, leaf litter, or in the trunks and branches of woody plants. Plasmogamy takes place by hyphal fusion between any two cells of the haploid hyphae with the appropriate mating type nuclei. This is obviously much more efficient, on this type of substrate, than spermatia requiring trans- port to the female structure. The life cycle has been reduced to haploid hyphae, dikaryotic hyphae, basidia and basidospores. The metabasidium or parasitic haploid plant of the ancestral basidophyte has been reduced to a single-celled basidium, scarcely recognizable as a generation in the life cycle.

The basidiocarp in at least the Hymenomycetes, is a newly developed structure produced directly by the dikaryotic hyphae for the efficient production and dispersal of the basidiospores. Thus the evolution of the various types of basidiocarps is very recent when compared to the extremely ancient evolution of the various types of ascocarps.

There has been a tendency to loose the forcible discharge of the basidiospores in many different groups of the Hymenomycetes. This has developed as a means of retaining the basidiospores in the basidio- carp for transportation by insects, rodents, or air currents after con- siderable delay. Except in the Phallales, this has usually resulted in a reduction in the basidiocarp morphology.

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MYCOLOGIA, VOL. 64, 1972

The Ustilaginales have very little in common with the Uredinales. Except for the metabasidium, the life cycle has also been reduced com- parable to that in the Hymenomycetes. There are no sexual structures. In species with the saprophytic stage, plasmogamy usually takes place between the budding haploid cells. Where there is no such saprophytic stage plasmogamy frequently takes place between different cells of the metabasidium so that there is no haploid generation except for the metabasidium.

In Phleogena (Auriculariales) the basidiospores are no longer forcibly discharged but remain in a dry powdery head raised on a stalk. This is clearly an end line modified for delayed dispersal of the basidio- spores.

While all of this is merely conjecture and may sound like science fiction, it is nevertheless, to me at least, so realistic that I firmly believe it. If I have not convinced all of you likewise, charge it to failure to communicate. I hope that I have at least provided all of you with something to think about.

LITERATURE CITED

Cain, R. F. 1948. Myriogonium, a new genus among simplified Ascomycetes. Mycologia 40: 158-167. . 1956a. Studies of coprophilous Ascomycetes 2. Phaeotrichum, a new cleistocarpous genus in a new family, and its relationships. Canad. J. Bot. 34: 675-687.

-. 1956b. Studies of coprophilous Ascomycetes 4. Tripterospora, a new cleistocarpous genus in a new family. Canad. J. Bot. 34: 699-710.

Hanawa, S. 1920. Studien uiber die auf gesunder und kranker Haut angesiedel- ten Pilzekeine. Jap. Z. Dermatol. Urol. 11: 14, 101-131.

Malloch, D. 1970a. New concepts in the Microascaceae illustrated by two new species. Mycologia 62: 727-740.

- . 1970b. The genera of cleistothecial Ascomycota. Ph.D. Thesis, University of Toronto. 672 p.

Savile, D. B. 0. 1955. The phylogeny of the Basidiomycetes. Canad. J. Bot. 33: 60-104.

Wells, D. E. 1954. Ascocybe, a new genus of lower Ascomycetes. Mycologia 46: 37-51.

White, W. L. 1942. A new hemiascomycete. Canad. J. Res. C, 20: 389-395. Winter, G. 1884-1887. Die Pilze. Ascomyceten: Gymnoasceen und Pyreno-

myceten. In L. Rabenhorst's Kryptogamen-Fl. Dutschl., Oesterr. und der Schweiz, 2 Auflage, Band 1, Abth. 2. Verlag von Eduard Kummer, Leipzig. 928 p.

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Issue Table of ContentsThe Journal of the Royal Asiatic Society of Great Britain and Ireland, (Oct., 1902), pp. i-iv, 733-966, 1-2, 1-32, 967-986Volume Information [pp. i-viii]Front MatterEvolution of the Fungi [pp. 1-14]Pileate Hydnaceae of the Puget Sound Area. II. Brown-Spored Genera: Hydnum [pp. 15-37]The Ultrastructure of Ceratiomyxa fruticulosa [pp. 38-54]Notes on Gymnoascaceae. II. Some Gymnoascaceae and Keratinophilic Fungi from Utah [pp. 55-72]Some Clavariaceae from Chile [pp. 73-80]Characteristics of an in Vitro Phenylalanine Incorporating System from Rhizopus arrhizus [pp. 81-91]Rediscovery of Mortierella rostafinskii and Mortierella strangulata [pp. 92-98]Mortierella umbellata, a New Species from Georgia [pp. 99-102]The Morphology, Taxonomy, and Sexuality of the Rice Stem Rot Fungus, Magnaporthe salvinii (Leptosphaeria salvinii) [pp. 103-114]Ultrastructure of Dormant and Germinating Conidia of Aspergillus nidulans [pp. 115-123]On the Identity of the Smut Tolyposporium eriocauli [pp. 124-128]Two New Species of Lambertella [pp. 129-136]Notes on Clavarioid Fungi. XII. Miscellaneous Notes on Clavariadelphus, and a New Segregate Genus [pp. 137-152]Axenic Growth and Nutrition of Gonatobotryum fuscum [pp. 153-160]Survey of Easter Island Soils for Keratinophilic Fungi [pp. 161-166]Undescribed Genera and Species of Harpellales (Trichomycetes) from the Guts of Aquatic Insects [pp. 167-197]Brief ArticlesEsterification of 4-C-Cholesterol by Phytophthora cactorum [pp. 198-199]Thermophilic Fungi of Some Central South Carolina Forest Soils [pp. 200-205]Morphology of Chromosomes in Ravenelia Species [pp. 205-207]Pistillaria fusiformis [pp. 208-212]Surface Structure in Allomyces during Germination and Growth [pp. 212-218]Antibacterial Activity Produced by Molds Commonly Used in Oriental Food Fermentations [pp. 218-221]A Method for Separating Aerial Hyphae from Surface Growth [pp. 221-223]Dibotryon morbosum: A Facultative Osmophilic Fungus [pp. 224-225]

ReviewsReview: untitled [pp. 226-230]Review: untitled [pp. 230-233]Review: untitled [pp. 233-234]

Back Matter