140 BOTANICAL GAZETTE [AUGUST 
of a layer 3 cells deep and disintegrates early. The spores lie in a 
mass of gelatinous material, the remains of the former tapetum, 
and scattered among them are many small, ill developed cells 
which show a tendency to break down. These are abortive pollen 
grains, or possibly in some cases abortive mother cells. 

FIGS. 42~47.—Richardia africana: fig. 42, embryo in early stage of development; 
¢, cotyledon; 5, stem tip; fig. 43, mature pollen grain previous to nuclear divisions; 
fig. 44, pollen grain previous to division of generative cell; fig. 45, male cells in con- 
tact; fig. 46, tube nucleus and male cells, the latter abnormal as to shape and com- 
Parative size; fig. 47, sprouting pollen grain. 
There is a great lack of uniformity in the divisions within the 
pollen grain. In one case (fig. 43) all were delayed until after 
dehiscence; but this is certainly very unusual. The first nuclear 
division, by which the generative nucleus is differentiated, usually 
occurs early. The generative nucleus does not surround itself 
with cytoplasm and a distinct cell membrane, but retains its nuclear 
character after division. Usually it divides before dehiscence 
occurs (fig. 45), although a number of grains were taken from 
