TAXONOMY 
293 
periods than now. They differ from the Angiosperms in several 
respects, viz.: they bear naked ovules on the edges or flat surfaces 
of leaves called carpels, while Angiosperms bear covered ones; each 
megaspore produces within itself a bulky prothallus, in the upper 
portion of which originate one or more archegonia, while in Angio¬ 
sperms no recognizable prothallus has been proven to exist; the 
stored food tissue within their seeds is prothallial tissue loaded with 
starch, etc., while that in Angiosperm seeds (endosperm) is developed 
from the endosperm nucleus; the mode of growth of their stems is 
always indefinite while that of Angiosperms is either indefinite or 
definite. 
Pig. 160.— Cycas revoluta, showing terminal bud of foliage-leaves just opening. 
(Gager.) 
The groups still extant are the Gycads or Fern Palms, the Gne- 
tums, the Ephedras, the Ginkgos and the Conifers. Of these the 
Conifers comprising over 300 species are the most numerous. Many 
of them yield valuable products to pharmacy and the arts. 
The Conifers include the pines, spruces, hemlocks, cedars, firs, 
arbor vitae, chamaecyparis, and larches. All of their number are 
evergreen except the larches, which drop their foliage upon the 
advent of winter. 
