EMBKYO-SAC OF GYMNADENIA CONOPSEA. 
15 
one or two tiers of four cells placed crosswise surmounting 
it ; from the method of formation and the fact that in some 
genera a canal-cell has been observed cut off from the oosphere 
and forced up between these cells, this rosette ” may be 
Fig. 4. — Diagram of wholly internal protliallium (so-called “ endosperm ”) 
of Conifer, with an archegonium, consisting of an oosphere (“ cor- 
pusculum,” “ secondary embryo sac ”), surmounted by a ‘‘ rosette ” 
of four cells, placed cross-wise ; between these a “ canal-cell ” is forced. 
A tendency to still further withdrawal within the macrospore (primary 
embryo sac) is indicated by the funnel-like depression. Pr. Primary 
embryo-sac at apex. Nuc. Nucleus of ovule. 
regarded as the neck of the archegonium. As seen in the dia- 
gram (Fig. 4) the archegonium is even more deeply withdrawn 
into the prothallus than was the case in Selaginella, and in 
some genera it becomes quite sunk into the prothallus. 
We may now inquire what processes and structures in such 
an ovule as that of Gymnadenia are related to those just 
reviewed. 
The first step appears to be to settle whether the ‘‘ embryo- 
cell of the Angiosperm is the equivalent of the oosphere 
of the Gymnosperm and Cryptogam. 
Warming and Vesque argue somewhat as follows : — The 
embryo-sac mother-cell becomes divided by various trans- 
verse walls, just as the subepidermal cells of an anther 
become divided by walls parallel to the epidermis to form 
pollen mother-cells.” Hence, the cells into which the 
embryo-sac mother-cell is cut up are so many spore mother- 
cells,” i.e. each is equivalent to a pollen mother-cell. Vesque 
says further, that two of these opposed cells form each a 
group of four nuclei in its interior, just as the pollen mother-cell 
forms four pollen grains in its interior, and that the cell-wall 
between the two tetrahedral groups becomes absorbed, and 
so eight nuclei are formed, in two groups of four each, at 
the respective ends of the embryo-sac so formed by fusion of 
the two mother-cells. 
