SEED-BEARING PLANTS 409 



angiosperm means "enclosed seed."^ The fundamental 

 distinction between gymnospermy and angiospermy was 

 first made clear by one of the greatest of English bota- 

 nists, Robert Brown, in 1827 (Fig. 10). 



363. Comparison with Fems.^ — The cycads resemble the 

 true ferns in several points — in the vernation of their 

 leaves (coiled in the, bud), in the venation of the leaves' 

 (forked veins), in the possession of sori (for microspor- 

 angia), in having multiciliate sperms, in having sporo- 

 phylls (megasporophylls) that closely resemble foliage 

 leaves, and in having the embryo dependent at first upon 

 the prothallus for nourishment, but later becoming 

 established as an independent plant. 



They differ from ferns in having the non-green gameto- 

 phyte dependent for nourishment throughout its Hfe 

 upon the tissues of the sporophyte. In the heterosporous 

 habit they differ from the true ferns, but resemble the 

 higher fern relatives, like Selaginella. Their greatest 

 step forward is the development of a seed. They are the first 

 true seed-bearing plants to be met with among living 

 species, as we ascend from the Algae. How closely 

 Selaginella approaches the formation of a true seed may 

 be seen by referring to the condition in the megaspor- 

 angium following fertilization (Fig. 284). If the female 

 gametophyte of Selaginella should remain within the walls 

 of the megaspore; if the embryo should undergo a period of 

 rest after the formation of the young stem and first leaves, 

 and if this entire structure should remain within the mega- 

 sporangium, we should have a true seed in Selaginella. 



The cycad seed is primitive (or imperfect as a seed), 



' From the Greek, angeion {hyytipv), a vessel -f- sperma {(riripiia), 

 seed. 



