214 



MORPHOLOGY 



n 



(belonging to the inner fleshy layer) 

 being suppressed. This is just the 

 reverse of the vascular condition in 



474 475 476 Ginkgo, in which the set of vascular 



FIGS. 474-476. Microsporophylls (sta- strands belonging to the outer 

 mens) of Taxaceae: 474, Podocarpus (after fleshy layer is suppressed, and the 



HOOKER); 475, Toxus (after RICHARD); ^ belonging to the inner fleshy 

 476, Torreya (after HOOKER). From J 



ENGLER and PRANTL. layer is developed. In early stages 



of the ovule the nucleus is entirely 

 free from the integument, but as the ovule 

 develops largely from beneath, the region 

 in which the nucellus and integument are 

 free from one another is carried to the tip 

 of the ovule. A notable change in the 

 ovule, as contrasted with the preceding 

 groups of gymnosperms, is that there is 

 no nucellar beak or pollen chamber (fig. 

 477); nor is there developed about the 

 megaspore mother cell any special diges- 

 tive (glandular) zone of cells, as in 

 Ginkgo. The development of the linear 

 tetrad and the selection of the innermost 

 megaspore for functioning are as usual. 



Female gametophyte. The female ga- 

 metophyte develops by the usual stages : 

 free nuclear division (up to 256 nuclei), 

 parietal wall formation, and centripetal 

 growth. It is important to note the 

 variation in the appearance of the arche- 

 gonial initials. In some cases they are 

 not differen dated until the gametophyte 

 has become quite extensive; that is, they 

 appear comparatively late in its history. 

 In other cases, however, notably in tions of ovulate strobilus of Tor- 

 Torreva. the archegonium initials appear r ^ a a s es s- 



the enveloping bracts and the soli- 

 as SOOn as Wall formation has filled the tary terminal ovule; upper section 



embryo sac with tissue (figs. 478, 479). ( the older ) shows the two integu- 



Archegonia.-The archegonia range ments , ( "' />' \ ucellus < w) ' * nd 

 d deep-placed mother cell. After 



in number from one to eleven, the neck COULTER and LAND. 



FIG. 477. Longitudinal sec- 



