454 BOTANICAL GAZETTE [JUNE 
The ovules are yet without 
placentae are still wholly undifferentiated (figs. rg and 15). 
integuments at a time when the 
microsporangia have a well marked tapetum and the sporogenous 
tissue has neared the spore mother cell stage (figs. 77 and 78). 
The initiation of the integu 
ments on the ovules occurs at the 
time of the tetrad stage of the 
microsporangia, or while the pol- 
len grains are separating and 
becoming round, and before the 
dominant megaspore has been 
determined. At this stage the 
microsporangium is inactive until 
the pollen is shed. 
THE MICROSPORANGIUM. 
In the development of the 
flower the second whorl of papillae 
to arise on the receptacle is that 
of the stamens. These papillae — 
early become stalked below, en- — 
larged and rounded above. In 
Typha this enlargement does not 
‘occur until much later. While 
the placenta. is still composed of 
: eR er Se 
% 7 
ies, = at 
fore the appearance of the 
ovules, the microsporangia have 
. attained their characteristic quad- 
_ rilocular form, and the epidermal = 
layer is separated from the hypo- — 
%. 
