1905. ] On the Cytology of Apogamy and Apospory. 467 
condition characteristic of an earlier phase of the heterotypical mitosis, which 
may throw some light on the anomaly. A discussion of these results 
will appear in the final memoir. It is interesting to note that Professor 
Strasburger has placed a similar interpretation on the phenomenon of 
apogamy in HLualchemilla,* which was first described by Murbeck. Here, too, 
there is no reduction either in the formation of the embryo sac or of the 
ovum, the latter giving rise, without fertilisation, to the apogamously formed 
embryo. 
The prothalli of the two apogamous varieties, Nephrodiwm pseudo-mas Rich. 
var. polydactyla Wills, and Nephrodiwm sseudo-mas Rich. var. cristata 
apospora Druery, exhibit two striking differences. "Whereas in the former 
nearly all the prothalli, except very young ones, have a strand of vascular 
tissue extending throughout the greater part of their length, in the latter only 
two cases of feebly-developed tracheides have been seen. Again, in 
Nephrodiwm pseudo-mas var. polydactyla, migrating nuclei, some of which 
have been seen to fuse, are a characteristic feature.t Out of a large number 
of prothalli it was found that about 73 per cent. of the young ones exhibit 
phases of nuclei passing from one cell to another. As this fern produces 
fertile spores, it is almost certain (it is hoped shortly to settle this point) that 
there is a true reduction during the division of the spore mother cells, the 
doubled number characterising the sporophyte is apparently brought about 
by the migration and fusion of prothallial nuclei. In Nephrodiwm pseudo- 
mas var. cristata apospora, out of 80 prothalli examined, only two showed 
possible cases of nuclear migration, and these were open to doubt as regards 
their interpretation. 
The reason for the absence of fusion in other cases is obvious, for the 
prothalli of Nephrodiwm pseudo-mas var. cristata apospora, as we have seen, 
already possess the full complement of somatic chromosomes. Hence there 
is no need for the fusion of two nuclei which, by their union, double the 
number of chromosomes. 
-I am deeply indebted to Professor J. Bretland Farmer, and to Mr. J. E. S. 
Moore for their constant help and advice. Professor Farmer has most 
kindly allowed me to use his material, and has superintended the work 
throughout. 
* E. Strasburger, ‘Die Apogamie der Hualchimillen,” ‘Jahrb. fiir wiss. Bot.,’ Leipzig, 
vol. 41, 1904, pp. 88 to 164, Pl. I to IV. 
t Farmer, Moore, and Digby, loc. cit. 

