430 Lang. — Studies in the Development and 
refractive and undistinguishable from one another ; these cells 
stain deeply and uniformly (Fig. 14). The number of cells 
that undergo this sterilization is not great, but the fact of its 
occurrence is of interest, for comparison with what takes place 
in the large sporangia of Pteridophyta, e. g. Equisetum 1 , 
Psilotum 2 , Ophiogtossum 3 , and in the pollen-sacs of some 
Angiosperms, e. g. Arum maculatum . The sterilized cells are 
always much smaller than the surrounding sporogenous cells 
with which they agreed in size before the change commenced. 
This circumstance, taken together with the fact of the 
sterilized cells being more or less flattened in most cases, 
suggests that increase of pressure within the sporangium is at 
least a factor in their production. It is of interest in regard 
to this to note that at the time of their appearance the 
epidermal layer has just acquired its thick walls, which may 
be presumed to offer greater resistance to the increase in size 
of the sporogenous mass within. It is possible that deficient 
nutrition may be another factor in their production, but their 
frequent occurrence close to the tapetum itself points to the 
operation of some other cause. 
The spore-mother-cells become isolated from one another. 
The tetrad-division was not followed in detail, but the tetrads 
still enclosed in the wall of the mother-cell closely resemble 
those of other Cycads. Fine granules are present between 
them, but only in small amount. The spherical spores, when 
they become free, do not nearly fill the cavity of the 
sporangium (Fig. 15). 
The tapetum persists as a complete layer within the wall 
of the sporangium ; its cell-walls have disappeared. The 
individual cells stain deeply ; each possesses a nucleus 
which never assumes the highly refractive appearance of the 
layer immediately outside. The nucleus often breaks up into 
two or three, apparently by fragmentation. 
1 Bower, Phil. Trans. 1894, p. 500, Fig. 21, PI. 43. 
2 Ibid. p. 550, Fig. 143, PI. 51. 
3 Rostowzew, Recherches sur TOph. vulg., note preliminaire, p. 28, Taf. 1 , 
Figs. 1,5. 
