Gametophyte of Selaginella. 423 
an accurate figure of this stage, but interpreted the nucleus 
as a nucleolus. Miss Lyon, in her work on S. apus and 
vS. rupestris , fully confirmed Fitting’s statement, and the 
writer has found the same condition to obtain in 5 . Kraus - 
siana. 
Fig. 1 shows a transverse section of a young spore of this 
species, made a short distance back of the apex. The primary 
nucleus was divided into four, these being much flattened. 
The very thin protoplasmic vesicle is still free from the 
mesospore. The nuclei continue to divide, but this takes 
place slowly, and does not keep pace with the rapid expansion 
of the protoplasmic vesicle, which soon becomes closely 
applied to the inner surface of the mesospore. The vesicle is 
so thin as to be scarcely discernible, except where it has 
become detached from the mesospore. The latter increases 
rapidly in size, the protoplasmic vesicle keeping pace with it, 
and finally the mesospore again comes into close contact with 
the exospore. The protoplasm is still reduced to an exceed- 
ingly thin film which may be very easily overlooked, and the 
nuclei are small and widely scattered. Neither at this stage, 
nor in any subsequent ones, are the nuclei in vS. Kraussiana 
confined to the apical region of the spore, as Miss Lyon states 
is the case in the species examined by her. 
The protoplasmic layer now begins to thicken rapidly, and 
the nuclei increase in number, and also become larger and 
lose their flattened form (Fig. 4). For some reason, possibly 
because the fixing process was slow, no karyokinetic figures 
were encountered in the earlier stages, but there is no 
reason for supposing that the division is amitotic, as Heinsen 1 
suggests. 
The structure of the nucleus is somewhat peculiar. Its 
contour is clearly marked and there is present a central 
nucleolus-like body which stains very strongly, but the rest 
of the nuclear cavity appears quite destitute of anything 
which could be interpreted as a nuclear filament or chromatin. 
In later stages (Fig. 14), the central mass sometimes appears 
1 1. c. p. 478. 
