Garnet op hyte of Selaginella. 
421 
The Spore-membranes. 
During its earlier stages, the growth of the massive and 
complex membrane is almost entirely due to the activity of 
the tapetal cells of the sporangium. As was pointed out by 
the writer 1 , the extremely small amount of protoplasm in the 
young spore could not account for the massive wall developed 
at a very early period. Fitting’s demonstration that the small 
and delicate protoplasmic vesicle of the young spore is almost 
free from the wall emphasized this, and the writer has been 
able to verify his results for S. Kraussiana , and Miss Lyon 
has done the same for .S. apus and X. rupestris. It is highly 
probable that all species agree essentially in this respect. 
The process is, in brief, as follows. The young spore shows 
a small globular vesicle near the apex, which is very evident 
in the fresh spore, and has the appearance of a large nucleus, 
for which it was taken until Fitting pointed out its true 
nature. This vesicle is the protoplast of the spore, and grows 
much more slowly than the membrane, between which and 
the protoplast a large cavity is developed (PI. XIX, Fig. 1). 
At an early stage, the thick membrane separates into two 
layers, the ‘ exospore 5 and ‘ mesospore ’ (Fitting). These are 
in contact at the apex of the spore, but the former enlarges 
more rapidly than the latter, and thus a second space is 
formed (Figs. 1, 2). The single small nucleus of the young 
spore divides at an early stage, and this division is repeated, 
the protoplasmic vesicle enlarging as the nuclear divisions 
proceed. 
At this stage (Fig. 1) the exospore in section appears as 
a thick, strongly staining layer, with marked sharp perinium 
or ridges upon its outer surface. These in X. Kraussiana 
form a reticulate pattern upon the outside of the spore. The 
mesospore (m) presents much the same appearance as the 
exospore, but is of nearly uniform thickness. It looks as if 
it were formed by the splitting off of an inner layer from the 
exospore. Miss Lyon, in her description of the spore-coats, 
1 1. c. p. 504. 
G g 2 
