342 BOTANICAL GAZETTE [NOVEMBER 
The number of chromosomes in Convallaria is quite large. 
A count in the nuclear plate stage showed eighteen segments as 
the reduced number. The same number may be counted during 
the subsequent resting stage and also after the second division. 
THE MICROSPORES. 
After the second division of the mother-cell nucleus the 
young pollen grains do not separate immediately, but remain a 
short time inclosed in the thickened walls of the parent cells. 
With little difficulty one can follow all the steps in the process 
of dissolution which these walls undergo. First the increasing 
sponginess of the already thick wall; a simultaneous differentia- 
tion of its inner layer destined to become the wall of the spore; 
and finally the complete solution of the outer part, leaving the 
young pollen grains united only by the intervening walls. These 
apparently split at once into two layers, thus freeing the mem- 
bers of the tetrad. : : 
The pollen grains at first are quite small, and possess thin 
purple-staining walls, finely granular cytoplasm similar in ane 
sistency to that of the somatic cells, and a highly chromatic 
nucleus which occupies about one fourth of the cell-cavity 
(fig. 23). The further changes are mostly normal. The pollen 
grains, which from the first are elliptical, gradually increase in 
size until their volume is more than doubled. The wall increases 
in thickness, and the whole grain assumes a bluer tinge with 
gentian-violet. 
A short time before the flower opens, the nucleus undergoes 
division, whereby a generative cell is cut off (fig. 24): shee 
cell is lenticular in form, and separated from the gencral ie! 
of the grain by a distinct cell wall. The generative nucleus 15 
exceedingly chromatic, so much so in fact that it stains ere 
homogeneous dark purple with the gentian-violet. The wren 
tive cell in Convallaria seems to differ from those in most of ne 
monocotyledons described by other writers in not sep 
an early period from the wall of the pollen-grain. It app y 
remains in all cases attached until the time of pollination. 
