certain Varietal a?id Hybrid Ferns. 209 
abnormal, and it may be that the disturbance of these relations, the 
upsetting of the K ernplasma - relation, lies near the root of the matter. 
But it is of course evident that this does not really explain anything, 
for what we want to know is just what it is that disturbs these normal re¬ 
lations. It is certainly not merely hybridism. The hybrid is indeed more 
sterile than the sport, but the phenomena are of the same order in the two 
cases. We find the same early degeneration in both, the same ‘ tubular 1 
nuclei simulating amitosis, the same irregularity in the distribution of the 
chromosomes on the heterotype spindle. We feel that it is of little use at 
present to endeavour to give explanations which can only rest on a very 
insecure base. But it is at any rate clear that the sterile ‘ sports ' demand 
far more attention than has hitherto been paid them, and we confidently 
anticipate that they will furnish important clues to the understanding of the 
causes of sterility in hybrids. Many of the remarkable deviations that are 
so characteristic of the cells, and especially of the nuclei, in malignant 
neoplasms, are also to be encountered in the aberrant cells of these sports 
and sterile hybrids. Whether the underlying causes are similar is still to 
seek, but we think that there is an interesting field of inquiry in this direc¬ 
tion, and one well worthy of investigation. As far as the immediate 
future is concerned, what is required is a greatly extended knowledge of the 
plain facts. 
We do not propose to discuss the questions that arise in connexion 
with the mode of formation of the heterotype chromosomes further than we 
have already done, but reserve this to be dealt with in a future communica¬ 
tion now on the way towards completion. 
Summary. 
1. The evidence from the study of the cytology of Polypodium 
Schneideri is consistent with the view that it is of hybrid origin, although 
it is not very conclusive if taken by itself. 
2. The nuclei of P. aureum are about two-thirds the diameter of those 
of P. vulgare and its var. elegantissimum. The number of chromosomes in 
P. aureum is about 34-36, in P. vulgare about 90, and there are about the 
same number in the variety elegantissimum . In P. Schneideri , the hybrid, 
there are variable numbers, the range lying between 95 and 125. 
3. The sporangia are apt to produce a large proportion of abortive 
spores in var. elegantissimum , and in the hybrid no fertile spores have been 
found. This sterility is to be associated with the degenerative changes in 
the cytoplasm, and these become especially acute at meiosis. The nuclear 
apparatus also appears to be, at least in part, responsible for the failure to 
form fertile spores. 
4. The achromatic spindle in P. aureum and some other species is 
P 
