112 BOTANICAL GAZETTE [ FEBRUARY 
layer forms the endothecium, which then lies next to the tape- 
tum, as in fig. 54. 
At the time of their first division, the pollen mother-cells are 
lying free in the cavity of the sporangium, and are perfectly 
spherical in form. The division occurs simultaneously in all 
the mother cells ina loculus, and it can frequently be noticed 
that the two outer loculi are slightly in advance of the inner 
ones of the same anther. For example, when the spindles in 
an inner loculus are in an equatorial plate stage, as in jig. 54, 
daughter stars will be found in the mother cells of the outer 
loculus. As may be seen from the figure just cited, the chromo- 
somes are nearly spherical, and it is very easy to count them, as 
the spindles lie in all possible directions. In favorable prepara- 
tions the number eight can be counted repeatedly, even with a 
comparatively low magnification. Reference has already been 
made to this as being the reduction number found in the develop- 
ment of the megaspore. 
The rapidity with which the second division follows the first 
may be inferred from the fact that even in the same loculus 
mother cells may be found, some of which show daughter stars 
of the first division, while in others one of the daughter nuclei 
may already have formed the spindle for the next division. The 
two spindles generally lie across each other, as in fig. 55, but 
they may sometimes be side by side. 
We may take figs. 54, 56, 57, 58, as showing the stages 
which may be found in four adjacent flowers along a radius of 
the head. The spines of the pollen grain appear soon after it 1s 
set free from the tetrad. For a time the spore exhibits a large 
vacuole, but this soon disappears. 
While these changes have been taking place the tapetum and 
middle layer have been disorganizing. In this way a plasma 1s 
formed which gradually distributes itself among the pollen grains. 
The nuclei of the disorganized cells are visible for quite a long 
time. This plasma finally collects around the spores (/i- 59) 
and is at last encrusted upon them as a sheath ( fig. 62); exactly 
comparable to the perinium of a pteridophyte spore. 
