434 Lang . — Studies in the Development and 
the other cells of the row, and contained a single nucleus. 
It increases rapidly in size, and its nucleus gives rise to 
a considerable number of daughter-nuclei, which are situated 
in a layer of protoplasm lining the wall In a further stage 
the embryo-sac is filled with the thin-walled tissue of the 
prothallus ; its wall is thick and cuticularized. Surrounding 
the large embryo-sac in this advanced stage is a layer, one to 
three cells in thickness, which is all that remains of the 
sporogenous tissue. This layer appears to be of the nature 
of a tapetal layer. It persists although the cells outside it 
are becoming crushed as the embryo-sac increases in size, and 
its cells, which are frequently elongated vertically to the wall 
of the latter, contain in many cases two or three nuclei. If 
derived, as seems probable, from the outermost cells of the 
sporogenous mass, its place of origin would resemble that 
of the tapetum in the microsporangium. Further observations 
are required on this and other points, but the brief account 
given above will serve to show that Stangeria agrees closely 
with Ceratozamia or Cycas in the development of the 
embryo-sac. 
Summary. 
1. The microsporangia are arranged in sori, the develop- 
ment of which is similar to Ceratozamia : sometimes the 
sporangia remain for some time united in pairs. 
2. The sporogenous cells, usually four in number, are 
derived by periclinal division from cells of the sub-epidermal 
layer. The superficial cells take no part in their formation. 
3. The tapetum arises, when the sporangium has attained 
a considerable size, from the outer cells of the sporogenous 
mass. Previously the inner layer of cells of the wall has 
given rise to a double layer of cells which assume peculiar 
characters. 
4. Isolated cells throughout the sporogenous mass undergo 
sterilization. 
5. The structure of the epidermal layer of the wall and the 
