lecture4 life cycle of plants
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1. Adaptation to living on land and the first land plants
2. History of evolution of major plant types
3. Alternation of generations
4. Moss life cycle
5. Fern life cycle
Alternation of generations in mosses and ferns
The land that land plants colonized was hostile to life. Soil development was minimal.
Land plants grow in an environment that does not support them.They require several adaptations to be successful:
mechanical strength for support,exposed light catching surfaces,anchoring system,conducting system for water,system for obtaining mineral nutrients,a way to restrict water loss in desiccating air,a means of reproducing and dispersing on land
1. Adaptation to living on land and the first land plants
An advantage of being small is that many of the requirements for living on land are minimized.
Close to the soil surface the environment can be almost aquatic – even if it does not rain continuously.
Then the principal adaptation required becomes the ability to withstand the dry periods between the wet.
Advantages of being small
Devonian plant
community
Devonian plant community found at Rhynie, in Scotland. A reed-like marsh, 370-380 million years ago.
Simple dichotomous branching
MAIN FEATURES
!5 to 30 cm tall
No roots
Stomata with guard cells
Most had a central vascular strand
Cuticle
Asteroxylon had leaves –without a vascular connection
Sporangia
Asteroxylon
Lycopodium
Lycopodium, club mosses, share many features with Asteroxylon, but they do have roots.
http://web.utk.edu/~flemin00/pteridology/pteridology.html
http://www.ansci.cornell.edu/cgi-bin/db2www/plant_indiv.d2w/PHOTO?keynum=36
Equisetum arvense
Horsetails: Equisetum
Vegetative and reproductive axis bearing sporangia
The ‘scouring rush’
History of plant groups
2. History of evolution of major plant types
Fig. 17.3A
Alternation of generations
Fig. 17.4
3. Alternation of generations
Fig. 17.5
4. Moss life cycle
Moss sporophyte
Top of capsule
Developing protonema
Moss antheridium and archegonium
Fig. 17.3A
Fern life cycle
Fig 17.6
5. Fern life cycle
Sporangia Polypodium spp
sori
sporangia
http://departments.bloomu.edu/biology/chamuris/concepts2/labimg.html
A sorus
Magnified sporangia
Polypodium spp
Sporangia
Developing spores
Gametophyte
Polypodium spp
Gametophyte
Developing sporophyte
Arrangement of sporangia on two ferns
In lines on a broadleaved type At the end of the leavesAdiantumAsplenium
Cibotium menziesii in habitat in Hawaii. Photo courtesy of Peter Richardson.
Cyathea australis with the uncurling croziers visible. Photo courtesy of Scott Ridges
Tree ferns
Jungle-like forests of the Carboniferous were dominated by giant ancestors of club mosses, horsetails, ferns, conifers, and cycads.
Most of the plant fossils found in the coals and associated sedimentary rocks show no annual growth rings, suggesting rapid growth rates and lack of seasonal variation in the climate (tropical).
Coal formation
Anaerobic conditions and periodic inundations of the sea
Early Carboniferous
Britain
Ice cap
EquatorAppalachians
Late Carboniferous
Britain
Ice cap
EquatorAppalachians
Fossil
Lepidophylloides
Lepidophylloides is the name assigned to the leaves of the Lepidodendron tree .
Rock Type: Gray shale
Age: Middle Pennsylvanian Period, approx. 312 million years.
http://www.clearlight.com/~mhieb/WVFossils/Lepidophylloides1.html
Sections you need to have read
17.1 17.2 17.3 17.4 17.5 17.6 17.7
Courses that deal with this topic
Botany 113 Plant Identification and Classification
Botany 350 Introduction to Plant Geography
Geology 203 Evolution of the Earth
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