THE HISTORY OF PLANTS 



413 



or no branches, longer leaves, and leaf scars in vertical rows. Another 

 giant of the coal forests was Cordaites (Fig. 26.12), a primitive seed plant 

 and forerunner of the conifers. It had soft wood resembling that of pines, 

 but its leaves were bladelike and from several inches to 6 feet long, while 

 its seeds were borne on branching stalks instead of in a cone. Some of the 

 largest cordaites had trunks that rose 80 to 90 feet without a branch; 

 their topmost twigs reached 120 feet above the ground. More familiar in 

 appearance were the many small trees, herbs, and vines with fernlike 

 leaves; some of these were true ferns, but a larger number were seed ferns. 

 In these dank forests dwelt the oldest known 

 winged insects and the primitive stegocephalian 

 amphibians. 



Permian changes in plant life. The third great 

 earth disturbance, the Appalachian revolution, 

 occurred during the Permian period at the end of 

 the Paleozoic era. Once more the continents rose. 

 Lofty mountain ranges were formed, and a world- 

 wide change in climate set in. Great ice sheets 

 covered parts of all the southern continents ; in the 

 northern hemisphere the climate became dry and 

 cold. The coal swamps disappeared, and before 

 the end of the Permian nearly all their character- 

 istic spore-bearing plants except the ferns had died 

 out. In their place came a flora of plants with 

 smaller, more leathery leaves, better adapted 

 to cold and drought, and probably derived from 

 the unknown upland plants of Carboniferous 

 times. There were many seed ferns, and ginkgoes 

 and various primitive conifers appeared. A new 

 flora of cold-tolerant plants, dominated by forms 

 called Glossopteris on account of their narrow 

 tongue-shaped leaves, spread over all the southern 

 continents. Like most of the other successful 

 Permian types these are believed to have been seed plants; indeed the 

 outstanding event of the time, so far as plants were concerned, was the 

 rapid increase of seed bearers and marked decline of spore bearers. The 

 reason for this seems evident. Possession of seeds gave the spermatophytes 

 a distinct advantage over the spore bearers in this time of stress, for 

 their gametophytes and embryos were protected and nourished by the 

 parent sporophyte plant, while their seeds could remain dormant through 

 periods of adverse conditions and use their food stores for rapid growth 

 as soon as the proper season arrived. 



Fig. 26.13. Two charac- 

 teristic leaves from the 

 Permian Glossopteris 

 flora. Glossopteris at left, 

 Gangamopteris at right. 



