8 BOTANICAL GAZETTE [JANUARY 
introduction of curved walls at the axial corners of the arche- 
sporium (fig. 47). While in no observed instance was the 
inclosure quite complete at this time, it was noted that a little 
later the cells on the axial side may divide (fig. 45), thus 
bridging the gap in the wall layer. Coulter (3) has shown that 
in Ranunculus a part of the tapetum may come from the sporoge- 
nous tissue. Rosenberg (12) finds in Zostera that the tapetum 
on both the inner and outer sides can be traced back to the 
divisions of the greatly elongated sporogenous cells. In Elodea 
these divisions of sporogenous cells on the axial side seem to be 
of common occurrence, and there is probably a regular contri- 
bution to the tapetum from the sporogenous cells in that region. 
In addition there may be a contribution to the diffuse tapetum 
on any side by the sacrificing of potential spore mother-cells to” 
the nutritive function. When the time of spore formation is at 
hand the functioning mother-cells are fewer than were the 
primary sporogenous cells, notwithstanding divisions may often 
take place among these tending to increase their number. The 
successful spore mother-cells become greatly enlarged before 
their division (fig. 47). A cross-section of the sporangium: at 
this time may show only one of these cells, the others having 
broken down, though commonly there are three side by side 
(jig. 46), and portions of four are often seen in a given section. 
The primary wall cells form a zone several layers of cells in 
thickness, of which the outer one only, the endothecium, persists 
until the discharge of the spores. 
THE MALE GAMETOPHYTE. 
The male gametophyte is considered to have begun with the 
spore mother-cells. Both the first and second divisions of the 
mother-cells are characterized by slender. curved spindles termi- 
nating at either end in the plasmatic membrane ( figs. 48, 49)- 
Such spindles have been figured by Strasburger (16) for Cerato- 
phyllum. Following the first division a delicate wall is formed, 
dividing the mass into two hemispherical cells. The nuclei of 
these daughter-cells are greatly elongated. The number of 
chromosomes was not made out with certainty, but is probably 
twelve for the gametophyte. 
