THE SPERMATOPHYTA 355 



anomalous desert plant. These are distinguished from other 

 members of the class chiefly by the possession of vessels or ducts 

 in the wood and by a marked reduction in the female gametophyte 

 somewhat similar to that which occurs among angiosperms. It 

 has been suggested that through forms related to the Gnetales, the 

 angiosperms may perhaps have arisen from the gymnosperms. 



Angiospermae or Angiosperms. — Angiosperms differ from 

 gymnosperms chiefly in the fact that their seeds are not directly 

 exposed to the air on the open surface of a scale but are 

 enclosed in a definite case or vessel, the ovary. 



With their 135,000 species, their highly perfected and typically 

 insect-pollinated flowers, their enormously diversified plant bodies, 

 their successful invasion of all habitats, and their assumption of 

 practically every mode of life exhibited by plants, the angiosperms 

 stand at the apex of the vegetable kingdom. They are a modern 

 group and have arisen in comparatively recent geological time. 

 Before the competition of this new, vigorous, and well-equipped 

 phalanx, the older vascular plants have been swept aside, most of 

 them to complete extinction, and the rest, with few exceptions, 

 to comparative insignificance. It is only the thallophytes, with 

 their specialization for aquatic, parasitic, and saprophytic habits 

 of life, that can compare with angiosperms in number of species 

 and individuals, and we must remember that were it not for these 

 higher seed plants, practically all saprophytes and parasites would 

 perish. The angiosperms are of primary importance as food 

 producers for animals and man. 



Since it is the members of this group which we have studied 

 almost exclusively in the earlier chapters of the text, it will not be 

 necessary to treat them here with as great detail as we have the 

 other branches of the plant kingdom. It will be worth while, 

 however, to bring together the essential features of the class as a 

 whole, that we may readily compare it with the other seed plants 

 and see it in its proper relation to the rest of the plant kingdom. 



Vegetative Structures. — The vegetative body is much diversified. 

 Seed plants not only include trees and smaller woody plants, (the 

 only growth forms displayed by gymnosperms), but they have 

 developed a new type, the herb, which is particularly well adapted 

 to temperate or semi-arid regions, since it is small and soft- 

 stemmed, produces flowers and fruit after a very short growing 

 period, and can survive winter, dry seasons and other unfavorable 

 periods either underground or in Ihe form of resistant seeds. 



