426 BOTANICAL GAZETTE [JUNE 
spindle could be predicted. Centrospheres were observed both 
in the mother cell and tetrad stages. 
THE MATURE SPORE. 
The microspore usually reaches its full size and the exine 
acquires its characteristic markings before its nucleus divides. 
During the growth which precedes this division the nucleus 
remains approximately in the center of the cell, but just before 
the division it often moves toward one end of the spore (fig. 4\. 
The position of the nuclei, however, often indicates that division 
has taken place without any such preliminary movement ( fig. 5)- 
Nearly all the mature microspores of L. tigrinum present essen- 
tially the conditions represented in figs. 5 and 6. The tube 
nucleus is larger and erythrophilous, while the generative nucleus 
is cyanophilous. The number and size of nucleoli vary, but asa 
rule the nucleoli of the tube nucleus are larger than those of the 
generative nucleus. The chromatin network of the tube nucleus 
is much finer and more irregular than that of the generative 
nucleus. 
Such cases as figs. 6-§ are common, and they give the 
impression that a wall is separating the generative and tube 
cells. When the generative cell is lenticular and pressed against 
the wall of the spore it is usually at one end ( fig. 6), but occa- 
sionally it is at one side ( fig. 7). The cytoplasm of the gener- 
ative cell was entirely free from starch except in one instance. 
Centrospheres were observed in connection with both the 
tube and generative nuclei. It is comparatively easy to demon- 
strate centrospheres with the generative nucleus on account of 
the uniformity in their position and the small amount of cyto- 
plasm in the generative cell. The tube cell is richly supplied 
with starch, which differs greatly in appearance as different 
stains are used. 
_ The foregoing applies to most of the pollen grains of the 
species studied, but occasionally an anther was found which 
showed very different conditions. The most common variation 
_ was the division of the generative nucleus while still within the 
