170 Farmer and Digby. — Studies in Apospory and 
of the type species. In this, as in many other characters, the present form 
stands about midway between the type and Col. Jones’s variety. It is 
difficult to give exact ratios, as the sizes of individual cells vary a good deal, 
but by making drawings in outline of the cells and nuclei of correspond- 
ing regions of prothallia and leaves, both of the varieties and of the typical 
plant, we have arrived at approximate values. We shall give the data 
in another paragraph (see p. 185). 
It is clear that in the case of Ath. Filix-f. clar ., Bolton, we meet 
with an example of what, in the absence of the aposporous origin of the 
prothallium, would be regarded as parthenogenesis, for, as in true partheno- 
genesis (if it really ever occurs), the egg gives rise to an embryo without 
fertilization. But in this instance the egg itself is abnormal in respect of its 
nuclear composition. The nucleus of a normal oosphere produced on an 
ordinary prothallium only possesses half the number of chromosomes 
characteristic of the sporophyte. That is, meiosis has intervened (at the 
spore-mother-cell divisions), and the premeiotic number of chromosomes is 
no longer present, but has become halved, owing to the peculiar mode 
of distribution of entire chromosomes (the allelomorphs of each pair) at 
meiosis. But in the case before us the meiotic phase has been omitted, and 
consequently the premeiotic number of chromosomes characteristic of the 
sporophyte is retained throughout the gametophyte and is present in the 
oosphere. The egg then cannot be regarded as the exact physiological 
equivalent of that produced by a normal prothallium. It already possesses 
the full number of chromosomes that normally would only be provided as 
the result of fertilization. Hence from the point of view of the nuclear 
constituents — at any rate as regards the chromosome contents — the act of 
fertilization would be superfluous, and indeed, unless some method of 
regulating the number of chromosomes other than by meiosis should become 
operative, it would be contrary to expectation. The possibility, however, 
of such regulation should not be overlooked, in the light of Nemec’s state- 
ments respecting the restoration of the normal number when this had been 
artificially modified, as in his experiments on anaesthetized roots. On the 
other hand, the study of many animal embryos, in which the number 
of normal chromosomes had in various ways been disturbed, clearly indicates 
that such a power of regulation is exceptional. Indeed it may be stated 
generally that, whatever number an embryo possesses on starting develops 
ment, this is retained as far as development proceeds. The few exceptional 
cases, resulting from polyspermy, only emphasize the individuality of the 
chromosomes. A survey of the facts at present available renders it difficult 
to see how an egg that had retained the premeiotic number of chromosomes 
could possibly become fertilized. 
We may summarize the facts connected with the development of 
Ath. Filix-f oemina var. clarissima , Bolton, as follows: — 
