1900] ° LIFE HISTORY OF SILPHIUM 113 
THE MALE GAMETOPHYTE AND FERTILIZATION. 
The pollen germinates in the anther. Three or four places 
for the exit of the pollen tube are present, and at the time of 
dehiscence the contents of the spore can be seen protruding 
slightly from each of them. Thetwo nuclear divisions by which 
the vegetative and generative nuclei, and the two sexual nuclei, 
arise, were not followed; but the difference in size and staining 
reaction in the stages found indicate that there is no deviation 
from the process as ordinarily described. The generative nucleus 
(g, fig. 59) is soon surrounded by a small quantity of hyaline 
cytoplasm, distinguishable from the more granular protoplasm 
of the rest of the spore. The nuclei of the two sexual cells 
(m, fig. 60) are smaller than the vegetative nucleus. At this 
stage practically no structure can be made out in any of the 
nuclei. The male nuclei usually stain less deeply than the 
vegetative nucleus. 
When first formed the male nuclei are approximately spher- 
ical, as in fig. 60, m. But in later stages their form undergoes a 
very remarkable change. The nucleus begins to be drawn out 
at one end, and soon becomes very much elongated. During 
this process the two nuclei generally lie side by side, and may 
finally become so long as to reach fully half way around the inte- 
rior of the pollen grain. Some of the stages are shown in jigs. 
Or, a-f, 62, 63. It will be seen that the somewhat sinuous form 
generally assumed frequently resolves itself into a spiral (jig. 
61,d,e). This change of form was found in three of the spe- 
cies studied, S. integrifolium, S. terebinthinaceum, and S. perfolia- 
tum, and might possibly have been discovered in the other two 
had they been as thoroughly investigated upon this point. The 
Structure of the nucleus was very difficult to make out, since, in 
sections less than row in thickness, so long a body was likely to 
be cut in pieces; and with this thickness of section the pollen 
grain would be cut through but once, and the nuclei were seen 
against a background of deeply staining spore wall. With the 
Most favorable light the nucleus can be seen to consist of a net- 
work with extremely fine meshes. The surrounding film of 
