616 



APPENDIX A 



home in tropical regions. They prefer moist, shady habitats, although some of the 

 species such as the bracken fern and the resurrection fern may grow in very dry 

 situations. Ferns attain their greatest size in the tropics, where certain species 

 are trees (Fig. 13.15) that may reach a height of 50 to 80 feet. The stems of such 

 tree ferns are erect, woody, and unbranched, often covered with persistent leaf 

 bases, from which the vascular bundles may project like spines, and with a cluster 

 of very large compound leaves at the top. Most ferns, however, have a horizontal 

 or short, erect underground stem (rhizome) from which the leaves rise singly or in 

 clumps (Fig. 13.14). 



The next two classes (Gymnospermae and Angiospermae) together 

 constitute the old division Spermatophyta (sperm a tof l ta; Greek, 

 sperma, "seed," and phyton, "plant"). Taken together these two groups 

 comprise some 133,500 species and include the dominant plants of the 



A 





Fig. A. 17. The Carboniferous lyeopod Lepidodendron. A, a spore-bearing cone. B, twigs, 

 leaves, and terminal cones. C, a leaf. D, a part of the trunk to show the leaf scars. E, a part 

 of one of the subterranean stigmaria or root-bearing branches. {Modified from Turtox chart, 

 courtesy General Biological Supply House, Inc.) 



modern world. Most of the familiar trees, shrubs, and vines, and nearly 

 all the plants economically important to man are spermatophytes. We 

 have already described in some detail (Chaps. IX-XII and XVII) the 

 structure and functioning of a seed plant and here need mention only 

 those features of the various groups that represent departures from the 

 basic pattern there discussed. 



Class Gymnospermae 



The Lower Seed Plants 



The gymnosperms form the second class of the subphylum Pteropsida, 

 or the first subdivision of the division Spermatophyta. The plants of this 

 group are distinguished from other seed plants chiefly by a difference in 

 their reproductive mechanism. The name gymnosperm means "naked 

 seed" and refers to the fact that the seeds are not formed in the ovaries of 



