1906] SHREVE—SARRACENIA PURPUREA 109 
tion of the walls of the pollen grain the cytoplasm of the tapetal cells 
becomes much vacuolated and the nuclei lose their chromatin; 
but at no time does the layer become broken. The parietal layers 
at the time of the tetrad division are three to five in number, the 
endothecium is thickened on its inner and lateral walls, and the 
epidermis is undifferentiated. The thickening of the endothecium 
walls takes places very late—simultaneously with the division of 
the pollen grain nucleus—the cells for some time previous to this 
being filled with starch. 
Dehiscence is by means of two longitudinal slits, each of which 
opens two pollen sacs of the anther. A deep crease runs between 
each pair of pollen sacs upon the two sides of the anther, penetrating 
to the point at which the two microsporangia lic nearest each other 
(fig. 13). At this point is a group of small cells reaching from one 
microsporangium to the other, the walls of which are thrown into 
creases and folds, and fail to thicken in the further development of 
the anther, as do the neighboring cells. 
The pollen mother cells apparently lie in the synapsis stage for 
several days. At their first division it is possible to count the chro- 
mosomes, the reduced number being twelve and their form short 
and blunt (fig. 8). 
The tetrad division is simultaneous, there being no formation of 
wall after the first division. After a short period of adherence in 
tetrads the pollen grains round off and acquire the coats. The 
mature pollen grain is marked with cight meridional grooves so as 
to resemble a muskmelon. Beneath the grooves the intine is several 
times thicker than between the grooves (jig. 11). While the pollen 
grain is yet within the anther the nuclear division takes place which 
gives rise to tube and generative nuclei (fig. 12). In this condition 
the grains are shed, the stamens nearest the ovary opening first, and 
the outer ones successively. 
OVULE AND MEGASPORE. 
The placental outgrowths which arise from the flat sides of the 
Ovary, at the point of juncture of the edges of the carpellary leaves, 
grow inward almost to the center of the ovary, and these I shall 
designate as the “main placental outgrowths” (fig. 14). Each 
