214 
MORPHOLOGY 
(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. 474-4 76. Microsporophylls (sta- strands belonging to the outer 
mens) of Taxaceae: 474, Podocarpus (after fleshy layer is suppressed, and the 
HOOKER); 475, Taxu, (after RICHARD); ^ be l ong } ng to the inner fleshy 
476, Torreya (after HOOKER). From 
ENGLER and PRANTL. laver 1S 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 differentiated until the gametophyte 
has become quite extensive ; that is, they 
appear comparatively late in its history. 
In other cases, however, 
FIG. 477. Longitudinal see- 
notably in tions of ovulate strobilus of 7V- 
/T-I ,, i ...... reya at different ages, showing 
lorreya. the archegomum initials appear ., , ., ,. 
' ' 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- 
4 i ' rrM. L. ments (it, of), nucellus (n), and 
Archegoma. The archegoma range , fc 
deep-placed mother cell. After 
in number from one to eleven, the neck COULTER and LAND. 
