eae 
190t] SPORANGIA AND GAMETOPHYTES OF SELAGINELLA 133 
megaspores, but, unlike the latter, separate from one another 
as soon as the exospore develops. As was the case with the 
female gametophyte, the sexual generation begins before the 
microspore has ceased growing. At the moment that the 
microspores separate from one another, each possesses a thick 
and a thin coat, a layer of protoplasm parietally placed, with 
one nucleus, and a central cavity filled with fluid (jig. 68). 
The nucleus increases in size and divides. This process often 
takes place in that part of the spore where one of the lateral 
ridges meets the hemispherical base (fig. 78). The proto- 
plasm increases in quantity and encroaches on the central vacu- 
ole. Granules of various sizes make their appearance in the cavity 
and in the surrounding protoplasm. These bodies stain pre- 
cisely like the nuclei and the more regular ones may be mistaken 
for them, as I frequently discovered in the early period of 
my own work (fig. 77). By precautions in decolorizing, the 
presence of nucleoli always distinguish the nuclei from the 
granular masses. These bodies are formed by the agglomera- 
tion of many smaller granules. One of the nuclei formed 
by the first division remains against the wall. It may grow 
larger and the protoplasm immediately surrounding it is some- 
what denser, but no wall separates it from the rest of the 
spore. This may be the vegetative prothallial cell (figs. 70, 
75). The other nucleus passes into the center of the spore. 
The protoplasm that envelops it sends out radiating processes 
that incompletely divide the spore cavity into irregular cham- 
bers, each of which is filled with granular masses of various 
sizes and shapes (figs. 76, 80, 81, 83). These strands of proto- 
plasm are continuous with a thin layer in contact with the 
endospore. The central nucleus with its envelope of proto- 
plasm divides into two cells which usually separate from each 
other (jigs. 79-83). By repeated division of each of these 
cells a complex results which consists of two uniform masses 
of sperm mother cells. There is no law of sequence which 
the cells follow in dividing, although the final product consists 
of cells very regularly arranged (jigs. 95-97). The male 
