1901] SPORANGIA AND GAMETOPAYTES OF SELAGINELLA 129 
its final volume when the sexual generation begins, thus over- 
lapping the asexual (fig. 44). The initial steps of the female ° 
' gametophyte development are the rapid expansion, without cor- 
responding increase in thickness, of the protoplasmic vesicle, 
and the division of its nucleus. The nuclei divide by karyoki- 
nesis, and with each successive division become larger (/fgs. 
45,46). The thick envelope surrounding the vesicle stretches, 
becoming proportionately thin as its surface increases, until it 
comes to lie against the inner surface of the exospore. At 
this stage it consists of two distinct layers, the endospore_and 
The gametophyte at this stage thus consists of (1) exospore, 
still growing, (2) mesospore; (3) endospore; (4) the proto- 
plasmic vesicle, consisting of a very thin and homogeneous 
layer of protoplasm applied to the inner surface of the endo- 
spore, in whose apical region are imbedded numerous large, 
ovate, flattened nuclei; and (5) a large central vacuole filled with 
a watery fluid in which are suspended many oil drops. 
Beyond the increase in the number of nuclei, which preserve 
about the same relative distance from one another, there is no 
further change until the spore membranes complete their 
growth. When the maximum size is reached, fibrillae arise in 
the protoplasmic vesicle at the apex, and radiate downward over 
its surface, blocking it off into irregular areas, each of which 
contains one or more nuclei (figs. 49, 52, 52). Simultaneously 
the protoplasm becomes invaded with masses of granular 
matter, and encroaches on the space occupied by the vacuole. 
Nuclear divisions take place radially, and so rapid is this 
process that frequently the spindle fibers of three and four 
generations of nuclei may be seen in a single section. The 
fibrillar radiations permeate the protoplasm, keeping pace with 
its increase in thickness. As the central vacuole diminishes in 
size, its contents change in appearance from an emulsion to a 
turbid fluid thickened with granules (fig. 53). The proto- 
plasmic fibrillae apparently are concerned with the distribution 
nt 
~» 
