201 
certain Varietal and Hybrid Ferns. 
are for the most part really abnormal, as is shown by the deficiency 
of cytoplasm which they contain, as well as by the deviations from the 
usual course of cellular changes which they exhibit. Relatively few of 
these cells succeed in forming spores, and when they do so the spores them¬ 
selves are commonly depauperate, and always barren. 
We pass now to the description of the cytological features of the 
development of the sporangia and spores. 
In the case of the sporangia which are destined to degenerate early, the 
nuclei of the cells are seen to change their character and to assume 
a gelatinous or mucus-like appearance. The cytoplasm diminishes and the 
cells die away. As we have already said, these lethal changes may involve 
the basal cell at the periphery of the placental epithelium on which the 
sporangium is borne. This cell represents the proximal portion of the 
primordial cell from which, distally, the sporangium is produced. 
When the development of the sporangium is not arrested so early, the 
tapetum is cut off from the archesporium in the usual manner, but it seems 
never to assume that strikingly nutritive and glandular character so generally 
associated with this tissue (see PI. XVII, Fig. 22). On the contrary, the 
cells rapidly become relatively poor in contents. It often happens that the 
nucleus—or nuclei—may be of large size, but the cytoplasm is small in 
amount and poor in appearance. The tapetum as a whole breaks down at 
an early stage, and by the time that the spore mother-cells are passing into 
synapsis the tapetal contents form a scanty plasmodial nucleated mass 
within the sporangial cavity. It is evident, we think, that the failure of so 
many sporangia to advance beyond the synaptic stage is to be directly 
connected with this weakening of the nutritive function on the part of the 
tapetum. It often happens that, despite the poverty of the tissue in ques¬ 
tion, the archesporial cells, up to the isolation of the spore mother-cells and 
the passage of their nuclei into synapsis, do not show marked signs of 
deviation from the normal course of development. Possibly their supply 
of nutrition may be less limited, or the demands on it less exigent, before 
the characteristic growth of the cell which marks the onset of the meiotic 
phase with its attendant nuclear changes. 
The spore mother-cells which enter on meiosis exhibit a dense synaptic 
contraction (PI. XVIII, Fig. 25) in which it becomes impossible to make out 
the detailed structure, but, as usual, this condition passes over into the open 
spireme in which the thread is very clear. There appear to be anastomoses 
between different parts of the thread as a whole, but a little later on the 
separate chromosomes can be identified. They are, from the time of their 
first appearance, somewhat abnormal. They give the impression of being 
badly fixed, but we believe this character is not really due to any such 
cause but to their actual nature. They are somewhat ragged in outline, 
and there are great differences in size, as well as of form, between them. 
