THE GYMXOSPERMS 359 



SWBDIVISKXN" I. THE GYMNOSPEKMS, OB, 



G YMNOSPERM^ 



345. The gymnosperms. The gymnosperms (meaning naked 

 seeds) are distinguished from the angiosperrns because their 

 seeds are borne exposed on the carpels. They comprise not 

 only the familiar cone-bearing trees, or conifers, generally with 

 needle-shaped leaves, such as the pines, spruces, firs, hemlocks, 

 larches, cedars, etc., but also the large-leaved cycads, the 

 straggling, shrubby Epliedras, the climbing Gnetums, and that 

 interesting Japanese tree Ginkgo. The gymnosperms contain 

 the most ancient groups of living seed plants, and the fossil 

 remains of primitive types are found in the Carboniferous Age 

 and even earlier periods, with those of the giant horsetails and 

 club mosses (see Cordaites, Plate VIII). The study of ancient 

 gymnosperms, together with a fossil group, Ptcridospermw, 

 intermediate between the pteridophytes and spermatophytes, 

 may throw much light on the origin of the seed and seed habit. 



The living groups of the gymnosperms comprise in all less 

 than 450 species, of which more than 300 are conifers and 

 about 80 are cycads. With the exception of the conifers, these 

 groups are hardly more than remnants of the ancient gymno- 

 sperm floras. But the conifers are a very successful group, 

 which still forms extensive forests in some temperate regions 

 and covers mountain sides and certain large rather barren areas, 

 although such forests are being rapidly cut off for timber. Of 

 the smaller groups the cycads are mostly tropical, the Epliedms 

 are chiefly desert plants, and the Gnetums tropical vines with 

 large-veined leaves. Like the horsetails and club mosses, the 

 Epliedras have for the most part developed peculiar life habits 

 under unfavorable conditions, and so have been able to avoid 

 total extinction by withdrawing as far as possible from compe- 

 tition with the more recent floras. 



This account can only consider the two largest groups, the 

 cycads and the conifers. 



