108 BOTANICAL GAZETTE [Auaust. 
group arises from a base which is distinct from the bases of the adjo 
ing groups, and is made up of the primordia of five to eight stamens. 
There is no suggestion of a pairing of the groups nor of their falling 
in two whorls. Upon the central flat surface has arisen the ovary, ‘ 
which at its base is pentagonal in outline, and at its apex is s 
to give rise to the placentae are upon the sides of the pentagon, whi 
shows each placenta to be made up of the edges of two carpellary 
leaves (figs. 2, 14). 
MICROSPORANGIUM AND MICROSPORE. 
destined to give rise to filament and anther. The latter portion — 
bears approximately the same outline in cross section as do the q 
mature anthers. The location of the archesporium is indicated at 
first only by the slightly greater size of the nuclei in the region of 4 
the four microsporangia (fig. 4), but soon comes to be more sharply 
defined by the concentric arrangement of cells in the region of the — 
future parietal cells. The archesporium is at this earliest recog 
nizable stage about six cells in cross section, but grows rapidly to 
about twelve ce'ls in diameter (fig. 5). Development proceeds in — 
the autumn to the differentiation of the endothecium, the two OF 
three parietal layers, and the pollen mother cells. There is yet 20 
distinction of definitive sporogenous cells and tapetum. In thi 
condition the stamens pass the winter. 
The elongated parietal cells do not contribute to the tapetum, 
but it is made up entirely from the isodiametric cells of the arche- 
sporium. The outer outline of the tapetal layer is continuous, 
the inner is irregular only to an extent which makes it in some places 
two cells in thickness and in other places three. The cells of the 
tapetum do not wander among the definitive sporogenous cells 
Shortly after the differentiation of the tapetum, and before the pollen 
mother cells are in the synapsis stage, the tapetal nuclei divide once 
by mitosis, and so far as observed once only. At the time of tetrad 
division the tapetal nuclei are enlarged, the chromatin is granular 
and scattered, and the nucleoli are large. At the time of the forma 
2 
