Plant Physiol. (1972) 49, 1007-1011

Lateral Movement of Water and Sugar Across Xvlem in

Sugarcane StalksReceived for publication December 3, 1971

T. A. BULL, K. R. GAYLER,' AND K. T. GLASZIOUDavid North Plant Research Centre, P.O. Box 68, Toowong 4066, Queensland, Australia

ABSTRACT

Laterally connected vascular bundles in the nodes of sugar-cane (Saccharum species cv. Pindar) stalks allow a rapidredistribution of water across the stalk should the vascularcontinuity be partly disrupted. Tritiated water supplied to theroots exchanged rapidly between the xylem and storage tissue sothat net movement up the stalk was slow. The half-time forexchange in a labeled stalk was about 4 hours so that theentire water content of a sugarcane stalk can turn over at leastonce in a single day. No rapid flux of sugar between xylem andphloem or xylem and storage tissue was detected. Functionalxylem contained only low sugar concentrations: less than 0.3%w/v in the stalk and less than 0.02% w/v in the leaf. Previousreports of high sugar levels (9% w/v) in sugarcane stalk xylemreflect some degree of xylem blockage followed by a slowequilibration with free space sugars in the storage tissue.

The path of water through a plant is generally consideredto involve passage through the root cortex to the xylem andthence as a continuous column through the stem to the leaves.In the leaves water passes from the xylem through the meso-phyll cells to the substomatal cavity. Such a path involves lat-eral transport in both the root and leaf but, apart from lateralredistribution of water in the stem when parts of the root sys-tem are subjected to reduced water potential (2, 12), there islittle evidence for substantial lateral water movement in thestem. Hulsbruch (9) stated that water follows the path ofleast resistance through the plant, but considered that lateralmovement from xylem elements of the stem was a minor com-ponent of the total flow.

Sucrose levels in the fluid expressed from xylem elements ofsugarcane may reach 8 to 9% w/v (7). Since transpirationrates in sugarcane commonly exceed 1 liter per stalk per daythis flow through the xylem would transport some 100 g ofsucrose to the leaves daily, which is 25 to 50 times more sugarthan could be produced by photosynthesis in the same period.The purpose of this paper was to investigate the movement

of water and sugars through sugarcane stalks in order to re-solve the above anomaly.

MATERIALS AND METHODS

Four distinct approaches were involved and the methodscan be summarized separately for each study.

1 Present address: Department of Biochemistry, Melbourne Uni-versity, Melbourne, 3000, Victoria, Australia.

VASCULAR ANATOMY

Stalks from field-grown sugarcane (Saccharum species cv.Pindar) were hand sectioned and stained with tissue specificstains (phloroglucinol and aniline sulfate-methylene blue) forobservations of vascular traces, particularly in the nodal re-gion. Further sections were retted by the technique of Lauben-gayer (10) to facilitate studies on the positions of intact vascu-lar strands.

DYE MOVEMENT

Sugarcane plants were grown in containers filled with aperlite-vermiculite mixture (1:1) and supplied with a completenutrient solution. When required, the containers were im-mersed in water and the stalks severed under water with asharp knife. The water surrounding the severed stalk base wasreplaced with an eosin solution and the plants exposed to sun-light in a glasshouse.

Three treatments were imposed to follow dye redistributionin the stalk. These were (a) an intact stalk; (b) a stalk with twoopposing lateral cuts within an internode; and (c) a stalk withthe two lateral cuts separated by a node. Within 5 min of ex-posure the leaves of the control plants were fully colored andall stalks were split longitudinally to observe dye distribution.

Similar treatments were applied to intact plants so thattranspiration rates could be monitored.

TRITIUM MOVEMENT

1. Uptake. Two liters of tritiated water (1-2 mc) wereadded to a plant growing in a container as outlined above.Free drainage was allowed, and the drainage water was pouredback into the container several times to provide uniform label-ing around the roots. The container and excess drainage waterwere sealed in a polythene bag so that transpiration could befollowed by weight loss.

Samples of transpired water were collected from individualleaves by sealing them into polythene sheaths for short periodsduring the day. Subsequently samples were obtained from leafxylem vessels by inserting microcapillary needles directly intothe vessels. Other plants were allowed to take up tritiated waterfor 3 hr and then harvested and plant sections extracted with70% (v/v) ethanol.

All samples (ethanolic extracts were decolorized with acti-vated charcoal) were counted in a 5-ml mixture of toluene-ethanol (2:1) containing 0.4% PPO and 0.01% POPOP, w/v.The liquid scintillation counter (Ecko Electronics) was set upat -20 C, in the dark. All containers were preadapted in thedark and a 30-min dark period was allowed following additionof the sample. Counting efficiency for tritium was 15% inclear containers.

2. Loss of Tritium. The roots of a plant were supplied with1007

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BULL, GAYLER, AND GLASZIOU

PLASTICCAP

I.= -.Z I PERI STALTICRESERVOIR PUMP

FIG. 1. Flow circuit for measuring stalk tissue free space andrate of exchange for tritiated water and "4C-sugar solutions. Stalksections were severed under water and rinsed to remove cell debris.Plastic caps with tubing attached were clamped over the stalk endsand the desired solution then circulated through the stalk by theperistaltic pump. Sequential samples could be taken from the reser-voir.

tritiated water for 3 days to obtain a labeled plant. Subse-quently the roots were rinsed with water to remove residualtritium and the plant was allowed to transpire freely. Tissuepunches (0.7 cm diameter X 1.0 cm long) were taken at regu-lar intervals from a basal internode and from the internodestwo and six nodes higher up the stalk. Similar diameter puncheswere taken from the first fully unfolded leaf. To minimize theeffect of vascular damage on later sampling, the stalks weresampled in an ascending spiral, and the leaf from the tip down-wards. Samples were immediately dropped into preweighedbottles containing 2 ml of absolute ethanol and reweighed;50-,ul aliquots of the ethanolic extracts were counted as out-lined previously.

3. Tissue Free Space for Tritiated Water. A section ofsugarcane stalk (about 60 cm long) was cut under water andthe ends trimmed with a razor blade to reduce xylem blockage.Plastic caps were clamped over each end of the stalk and con-nected with water-filled tubing (1-mm bore) to a peristalticpump via a small (1 ml) reservoir (Fig. 1). Water was pumpedthrough the stalk and the reservoir replenished until any waterdeficit had been overcome. The tubing and reservoir wereemptied, refilled with tritiated water (0.5 mc in 3 ml) and thepump was restarted. Aliquots (10 [Il) were taken regularlyfrom the reservoir and diluted with 2 ml of ethanol for subse-quent counting.

SUGAR IN XYLEM AND LATERAL TRANSPORTOF XYLEM SUGAR

Cane stalks were cut and microcapillary tubes inserted intoindividual xylem elements at the apical end of the stalk withthe aid of a microscope and micromanipulators. A slight posi-tive pressure was applied at the basal end of the cut stalk orleaf, and the fluid entering the microcapillary tube was usedfor sugar analysis. By forcing an eosin dye solution throughfrom the basal end and measuring the volume of fluid enteringthe microcapillary tube before the appearance of the dye, itwas possible to calculate that it was near that expected from axylem element of the length of the stalk section being sampled.The method described to measure the free space with which

tritiated water equilibrated when pumped through the vasculartissue (Fig. 1) was also used to measure the free space for 14C-glucose and fructose. In one such experiment 14C-glucose solu-tion was circulated for 4 hr, and samples (10 ,d) removed atintervals for chromatography and liquid scintillation counting.Radioactive sugars were separated chromatographically andestimated by methods described previously (11).

RESULTS AND DISCUSSIONVascular Anatomy. The vascular anatomy of sugarcane has

been examined in detail previously (1) but not for the specificpurpose of examining water movement. Although the numberof vascular bundles in internodes along a sugarcane stalk re-mains constant there is considerable bifurcation and anasto-mosing in the node. At the point of leaf sheath insertion severallarge bundles and bundle branches laterally traverse the nodeto supply the sheath. Peripheral bundles also provide branchesfor the sheath. Immediately above this zone there is a regionof much finer lateral bundles arising as branches from thevascular elements of vertical bundles. These fine bundles ram-ify through the node and interconnect the vertically orientedbundles.

Although leaf sheaths have well developed connections withthe stalk vascular system, this is not true for either germinatingbuds (side shoots) or sett roots which arise from the band ofroot primordia associated with the node during germination ofstalk cuttings (setts). The vascular system of buds or sett rootsexists as root-like intrusions into the stalk. These intrusionsbecome tightly appressed to the stalk vascular bundles but donot become connected.

It is evident that two types of water movement must occurin the node region. First, the lateral bundle system allows a

rapid redistribution through coherently connected xylem ele-ments should vascular damage occur below the node. Secondly,water flow to side shoots and sett roots involves, initially atleast, a lateral flow across cells of closely appressed bundles.

Despite the complex branching present in the nodes therewas no evidence of bundle termination in young cane stalks.However, with increasing maturation and the dehiscence ofolder leaf sheaths the vascular elements supplying these sheathsmust become sealed. This will provide sections of vascular tis-sue above the last branch point which are no longer active inwater transport through the plant. These sections would beexpected eventually to reach steady state sugar levels similarto those in the surrounding parenchyma free space.Dye Movement. The simple experiment outlined in Figure

2 was undertaken to verify the role of the lateral bundles whichramify through the nodes. With no vascular damage the dyemoved rapidly through the stalk to the leaves. If the two op-

a.

I,LtS L

Il

b. C.

FIG. 2. Path of eosin through the vascular bundles of detachedsugarcane stalks. Stalks were severed under water and then treatedas follows (a) stalk intact (control), (b) two opposing lateral cuts(LC) were made within an internode, and (c) two opposing lateralcuts were made in adjacent internodes. Eosin solution was placedround the severed base of each stalk and a period of transpirationwas allowed. When eosin was observed in the leaves of the controlstalk all stalks were split longitudinally to observe the distributionof eosin. Those bundles (VB) containing eosin at the close of theexperiment are depicted.

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LATERAL MOVEMENT OF WATER AND SUGAR

posing cuts were separated by a node the dye moved up theundamaged part of the stalk to the node. At the node it was

redistributed laterally and moved up the undamaged sectionon the opposite side of the stalk. The following node served toredistribute the dye across the entire stalk cross section so thatall vascular bundles then carried the dye. However, if the twocuts were made within the same internode vascular continuitywas lost and no dye movement occurred.

That the dye movement represented water movement was

verified by the transpiration measurements made on intactplants (Table I). The presence of a node between the two cutsallowed about 60% of the total control transpiration rate butat lower radiation flux densities there was little difference intranspiration. When the two cuts were made within an inter-node transpiration was maintained for almost 2 hr and thenvirtually ceased. The initial water loss in this treatment (90 g)was about 10% of the stalk fresh weight. Consideration of thexylem volume (about 3% of stalk volume) and the volume ofstalk above the highest cut (about 50%) revealed that only15% of the water lost could have come from the xylem. Theremaining 85% must have been extracted from leaf and stalktissue before stomatal closure was effective.

Tritium Movement. Assay of the tritium activity in trans-pired water showed that after 3 hours transpiration the specificradioactivity was only 12% of that supplied to the roots, de-

Table I. Transpiration2 Rates in Sugarcane Stalks with LaterallyOpposed Cuts

The treatments illustrated in Figure 2 were imposed at 0830 hr,so that 30 min elapsed before measurements commenced. Transpi-ration rates were monitored by following weight loss. Solar radia-tion was measured with a Kipp thermopile connected to an in-tegrator.

TreatmentTime Solar Radiation

1 2 3

hr g HI20 dm-2 hr'I cal cr'2 hirl

0900-1000 2.3 1.9 1.8 321000-1100 2.7 0.9 2.3 401100-1200 4.6 0.2 2.2 681200-1300 2.9 0.3 1.1 421300-1400 2.7 0.2 2.7 431400-1500 2.3 0.2 2.2 301500-1600 2.3 0.2 2.3 24

0900-1600 3.1 0.5 2.0 44

Table II. Tritium Activity Recovered in Water Transpiredfrom theFirst Fully Expanded Leaf of Sugarcane

Two liters of tritiated water (850,c/l) were supplied at 0930 hrto the roots of a sugarcane plant growing in perlite-vermiculitemedium. Transpired water was collected as condensate in a poly-thene sheath placed over the leaf for about 10 min at regular inter-vals. Rate of transpiration was measured as cumulative weightloss.

Time Specific Radioactivity' Transpiration

uc/lifer g/plant

1000 2 2121030 0 3261100 5 4661230 104 726

<5,Ac/liter: not significant.

Table III. Tritium Activity Recovered from Transpired Water anzdXylem Vessel Contents of the First Fully Expanded Leaf

of SugarcaneTwo liters of tritiated water (1.1 mc/liter) were supplied at

0900 hr to the roots of a sugarcane plant growing in perlite-vermic-ulite medium. Transpired water was collected as condensate in apolythene sheath placed over the leaf for about 10 min. Xylemcontents were sampled by inserting a microcapillary directly intoleaf xylem vessels exposed by removing the terminal portion ofthe leaf.

Time Origin of Sample Radioactivityc

Ac/liler

1000 Transpired water <31300 Transpired water 3301500 Xylem contents 1000

1 <5 Ac/liter: not significant.

Table IV. Locationi of Tritiated Water in a Sugarcane Plant ThreeHours after Application to the Roots

Two liters of tritiated water (800 Ac/liter) were supplied at 0900hr to the roots of a sugarcane plant growing in perlite-vermiculite.Three hours later the plant was harvested and sections extractedwith 70%0 v/v ethanol. Ethanolic extracts were decolorized withactivated charcoal prior to scintillation counting. Leaves havebeen numbered successively down the plant from the first fullyexpanded leaf (0). Internodes have been numbered successivelyup the plant from ground level.

Plant Section Specific Radioactivity,

pc/liler

Leaf 0 1Leaf 1 2Leaf 2 1Leaf 3 1Apical meristem 4Internode 10 1Internode 8 6Internode 6 17Internode 4 33Internode 2 95Basal internode 190

1 <5 sc/liter: not significant.

spite the loss of over 700 g of water (Table II). Over 6 hourselapsed before the specific radioactivity of tritium in the leafxylem contents reached that at the roots (Table III). Duringthis period the volume of water transpired was almost equalto the stalk volume, i.e., some 33 times the xylem volume.The pattern of tritium distribution 3 hours after supplying

tritiated water to the roots showed that significant activitycould only be detected up to eight internodes (1.5 m) aboveground level (Table IV).

These results are consistent with the hypothesis that waterin the xylem is in rapid equilibrium with water in other parts ofthe stalk, the rate of exchange being sufficiently rapid to dilutethe radioactivity of tritiated water moving up the xylem to theleaves.An estimate of this exchange rate was obtained by measuring

the rate of loss of tritium from a labeled stalk. In all threeinternodes examined the half-time for tritium loss was about4 hr (Fig. 3). Results from the leaf were erratic due to lowcounts and altered transpiration rates arising from changes in

Plant Physiol. Vol. 49, 1972 1009

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BULL, GAYLER, AND GLASZIOU

0

TIME (BHOUR)+6

B+25

a~~~~~~~~~cr. ~~~~~~~~~~~~~LEAF

TIME (HOURS)

FIG. 3. Rate of loss of radioactivity from a stalk labeled withtritiated water. Stalk punches (0.7 cm diameter X 1.0 cm) weretaken in an ascending spiral from the basal internode (B) and frominternodes situated two (B' + 2) and six (B + 6) nodes further upthe stalk. Leaf punches (0.7-cm diameter) were taken downwardsfrom the tip of the first fully expanded leaf. All samples were im-mediately dropped into preweighed bottles containing 2 ml of ab-solute ethanol. Ethanolic extracts were decolorized with activatedcharcoal before scintillation counting in the dark at -20 C. Thehalf time (ti) for loss of radioactivity is shown for each internode.

730

o

E 60

>- 40

405 204

0 20 40 60 80

TIME (MINUTES)FIG. 4. Rate of equilibration of tritiated water in a sugarcane

stalk section with a displacement volume of 350 ml. The methodused is outlined in Figure 1. The initial rapid loss and recovery ofradioactivity reflects a pulse of unlabeled water remaining in thesection when the reservoir and tubing were filled with tritiatedwater. Initial and final counts were 733,400 and 6300 cpm/ml. Thedilution was therefore from 3 to 349 ml of which 3 ml was due totubing and reservoir. Hence, the tissue free space for tritiated waterwas 346 ml or 99% of the tissue volume.

leaf presentation to incoming radiation. Tritiated waterpumped through a stalk section reached a steady state concen-tration in less than 1 hr and the calculated free space volumewas almost equal to that of the section (Fig. 4).

It is evident that in sugarcane, the xylem water is in rapidequilibrium with water in the remainder of the stalk. Trans-piration involves not only water moved up the xylem vesselsbut water moved up the entire stalk free space. During a singleday's transpiration the entire water content of a sugarcane stalkcan be turned over at least once.

Sugar in Xylem and Transport of Xvlem Sugar. Hawker (7)

Table V. Conicenztrationi of Sucrose ini Xylem Vessels ofSugarcane Stalks

The 6-month cane was grown in a greenhouse at 28 C beforetransfer to 16 C to slow growth and increase sucrose content.Average contents were 10% w/v for the greenhouse cane and 17%ow/v for the one-year field-grown cane. Stalks were cut under waterand a slight positive water pressure was applied to the base to forcexylem contents into the microcapillary inserted into a vessel atthe top of the stalk. In method A the rind was removed from about5 cm of the top of the stalk and parenchyma was stripped to exposethe vascular bundles. In method B the top of the stalk was severedat a slight angle and the microcapillary inserted directly into avessel.

Sampling Growth Conditions Xylem CommentsMethod Sucrose Cmet

% W/vA 6-month green- 0.5 16-hr dark prior to sampling

house, cv. 7.0 16-hr dark prior to samplingPindar 1.0 24-hr dark prior to sampling

0.1 48-hr dark prior to sampling0.2 48-hr dark prior to sampling9.5 120-hr dark prior to sampling

A 6-month green- 0.38 Cut after several hr in light;house, cv. 0.39 sequential 2,u1 samples fromPindar 0.33 the same vessel.

A 1-year field- 7.0 Cut after several hr in light;grown, cv. 7.9 sequential 2,ul samples fromTrojan 4.3 the same vessel.

4.3

B 1-year field- 9.3 Cut 1400 hr. sunny daygrown, cv. 6.0 Cut 1500 hr, sunny dayTrojan 1.0 Cut 1500 hr, sunny day

3.0 Cut 1500 hr, sunny day0.3 Cut 1500 hr, sunny day

I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

0E0x

Ec.0

v

00

4

2

0 100 200

TIME (MIN)

FIG. 5. Rate of equilibration of "4C-glucose flowing through asugarcane stalk section. Method as illustrated in Figure 1. A stalksection having a 225-ml displacement volume was flushed withwater for 45 min at a flow rate of 1.5 ml/min. A 1.0% w/v solutionof "4C-glucose (5.1 ml) was then introduced into the reservoir. Theinitial and final sample counts were 3500 and 1080 cpm. The dilu-tion was therefore from 5.1 to 16.5 ml, of which 4.6 ml was due totubing and caps. The glucose free space of the stalk sections was6.8 ml or 3.0% of tissue volume.

I.

3

. __*w

a I a I0

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LATERAL MOVEMENT OF WATER AND SUGAR

measured xylem sugars in cane stalks by applying air pressureto the base of stalk sections. The droplets appearing at theends of the vascular strands were collected and combined foranalysis. The protruding strands were washed to avoid con-tamination by sugar from damaged cells, and dried with filterpaper prior to the application of pressure. Relatively highlevels of xylem sugar (8 to 9% sucrose) were measured.

If the xylem sugar was 9% (w/v) in a stalk transpiring aboutone liter water per day either 90 g sugar would be moved tothe leaves, or would be reabsorbed prior to moving into theleaves. A generous estimate for the amount of active growingtissue at the stalk apex is 200 g. At the maximum rate of sugaruptake of 1 mg/g fresh weight/hr that has been observed ex-perimentally from saturating glucose solutions (11), about 5 gof sugar could be removed by this tissue in a day. In any casesugar does not accumulate above about 2% (w/v) in caneleaves, and the net flux of sugar is normally towards the baseof the stalk.The anomaly generated by Hawker's results could be ex-

plained in several ways. First, the droplets sampled may nothave originated from the xylem. Secondly, the stalks used mayhave been taken from environments in which little transpirationwas occurring so that even a slight leakage of sucrose intoxylem could eventually give the high level observed. Finally,there could be a very rapid flux of sugar between xylem andphloem, such that sugar moving upwards in the xylem wasreconcentrated into the phloem and moved back down thestalk. If there were also a rapid lateral flux of sugar betweenconducting and nonconducting tissue, xylem flow could be animportant component in the distribution of sugar throughoutthe plant.

Sampling stalk xylem elements directly by the insertion ofmicrocapillaries partially confirmed Hawker's results, in that9% (w/v) sucrose was observed in 1-year-old cane containingabout 17% sucrose in juice, but in the same cane, the sucroselevel in some elements was as low as 0.3% (w/v). In youngercane the levels in six different stalks were less than 1.0% (w/v)but in one stalk the single xylem element sampled contained7% (w/v) sucrose. A xylem fluid sample from a stalk left inthe dark for 5 days contained 9.5% (w/v) sucrose (Table V).High sucrose levels could not be detected in leaf xylem ofeither of the varieties used for stalk xylem samples, the levelsalways being less than 0.02% (w/v) in more than 20 measure-ments of midrib and lamina xylem elements.To test the dynamic flux model of rapid sugar movement

between xylem and phloem, advantage was taken of previousobservations by Bieleski (3) that the phloem of isolated vascu-lar tissue from cane stalks accumulated glucose at rates atleast ten times higher than parenchyma cells, and by Hatchand Glasziou (6) that glucose and fructose are rapidly con-verted to sucrose during translocation. If radioactive glucosewas circulated through xylem in a closed system by the methodused for tritiated water (Fig. 1) then according to the dynamicflux model, the glucose should move across to the phloem, beconverted to sucrose, and at least some should re-appear inthe circulating solution as radioactive sucrose.The result of such an experiment is shown in Figure 5. The

volume of the tissue with which the "C-glucose equilibratedrapidly was 3% in contrast to 99% for tritiated water (Fig. 4).Chromatography of samples from the circulating solution upto 4 hours after adding glucose revealed no trace of radioac-tivity in sucrose, fructose or hexose phosphates. If glucosepenetration to the storage tissue had occurred, then accordingto the data of Hawker and Hatch (8), the amount of stalk tis-

sue present was sufficient to accumulate actively at least halfof the glucose supplied during the first hour.

There was a very slow loss of "C-glucose after the initialrapid change (Fig. 5) and chromatography revealed the appear-ance of nonradioactive sucrose in the circulating solution.However, when the system was changed to flow the solutionacross the cut ends, but not through the stalk section, the same

steady state level of sucrose was attained regardless of whichway the solution was flowed. We attribute the slow uptake ofglucose and leakage of sucrose to the storage parenchyma cellsexposed at the cut ends.

In a similar experiment, the free space volume for "C-fructose was 3.3% of tissue volume. Hawker (7) estimated thexylem and bundle sclerenchyma by microscopic examinationas constituting 7.5% of tissue volume, so it is virtually certainthat the glucose and fructose solutions used in these experi-ments circulated through xylem only.

Discounting that sucrose but not glucose or fructose canmove readily in and out from xylem, it is apparent that thereis no rapid flux of sugar between xylem and phloem, or xylemand storage tissue. However, although the permeability ofxylem elements to sugars is low, the sucrose concentration mayapproach that in the free space of adjacent tissue if watermovement through the element is blocked by damage or leafsheath dehiscence. The free space of storage tissue includes cellwalls and may attain sucrose concentrations similar to those ofthe cell vacuoles (5, 7). It appears that for much of the time,the capacity of the stalk to conduct water to the leaves is inconsiderable excess of transpirational losses, and the mainflow would be expected through xylem paths offering least re-sistance. These xylem elements should contain very little sugar.By promoting excessively high growth rates at the top of

the stalk, it is possible to drain bottom internodes of theirsucrose (4). It is problematical whether the reversal of thenormal sugar flow occurs via the phloem, or whether xylemsugar movement as suggested by Hawker (7) accounts formuch of the sugar redistribution.

Acknowledgment-We wish to acknowledge the technical assistance providedby Mr. H. Kirkman.

LITERATURE CITED

1. ARTSCHWAGER, E. 1925. Anatomy of the vegetative organs of sugarcane. J.Agr. Res. 30: 197-241.

2. BAKER, D. A. AN-D J. A. MILBaUN. 1965. Lateral movement of inorganicsolutes in plants. Nature 205: 306-307.

3. BIELESKr, R. L. 1958. The physiology of sugarcane. IL The respiration ofharvested sugarcane. Aust. J. Biol. Sci. 2: 315-328.

4. GLASszIou, K. T., T. A. BUJLL, M. D. HATCH, AND P. C. WHITEMAN. 1965.The physiology of sugarcane. VII. Effects of temperature, photoperiodduration, and diurnal and seasonal temperature changes on growth andripening. Aust. J. Biol. Sci. 18: 53-66.

5. GLASZiou, K. T. AND K. R. GAYLER. 1972. Sugar accumulation in sugarcane.Role of cell walls in sucrose transport. Plant Physiol. 49: 912-913.

6. HATCH, M. D. AND K. T. GLASZIOU. 1964. Direct evidence for translocationof sucrose in sugarcane leaves and stems. Plant Physiol. 39: 180-184.

7. HAWKER, J. S. 1965. The sugar content of cell walls and intercellular spacesin sugarcane stems and its relation to sugar transport. Aust. J. Biol. Sci. 18:959-969.

8. HAWKER, J. S. AND M. D. HATCH. 1965. Mechanism of sugar storage bymature stem tissue of sugarcane. Plant Physiol. 18: 444-453.

9. HwLLSBRUCH, M. 1956. Die Wasserleitung in Parenchymen. In: W. Ruhland,ed., Encyclopedia of Plant Physiology, Vol. 3. Springer-Verlag, Berlin. pp.520-540.

10. LAUBENGAYER, R. A. 1949. The vascular anatomy of the eight-rowed ear andtassel of Golden Bantam sweet corn. Amer. J. Bot. 36: 236-244.

11. SACHER, J. A., MI. D. HATCH, AND K. T. GLASZIOU. 1963. Sugar accumulationcycle in sugarcane. III. Physical and metabolic aspects of the cycle in im-mature storage tissues. Plant Physiol. 38: 348-354.

12. WEST, D. W., W. K. THOMPSON, AND J. D. F. BLACK. 1970. Polar and lateraltransport of water in an apple tree. Aust. J. Biol. Sci. 23: 231-234.

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