SUBKLNGDOM SPERMATOPHYTA 



339 



seminiferous scale has been much discussed, but it is probably to be 

 considered as an outgrowth of the sporophyll, perhaps comparable to 

 the placenta of the Angiosperms. In the Abietinese the seminiferous 

 scales become very much developed, and form the hard, woody scales 

 of the ripe cone. 



B 



C 



FIG. 304. Taxus baccata. A, section of the nucellus of a very young ovule (x 150) . 

 B, sporogenous tissue from an older ovule. C, an older stage showing young em- 

 bryo-sac (macrospore) (x 200). J), an older stage, with numerous free nuclei. 

 E, F, cell-formation in the young gametophyte (X 500). 



The young ovule is a nearly hemispherical body, about which, at a very early 

 stage, is developed the single integument (Fig. 305, C). The sporogenous tissue 

 may be traced, in some cases at least, to a group of cells which are the lowest 

 members of rows of cells, probably derivatives of single hypodermal cells. These 

 sporogenous cells enlarge, and usually divide into two or four cells, the young 

 macrospores, or embryo-sacs. Sometimes but a single one of these develops ; but 

 in Sequoia (Fig. 305) several of the embryo-sacs begin to develop, although only 

 a single one reaches maturity. 



Female Gametophyte. The primary nucleus divides repeatedly, the nuclei 

 being arranged about the wall of the young embryo-sac (Fig. 304, D). Between 



