1 88 Farmer and Dig by. — Studies in Apospory and 
to errors of counting. And although in the plants now under discussion 
it is impossible to speak with absolute certainty as to the degree of error 
that is unavoidably present, such a case as that of Lastrea cristata apospora 
is well worthy of attention. Since the estimation of the chromosomes 
in the prothallium, with two exceptions, all fell between 59 and 64, with 
a great preponderance in favour of the former, we think we are probably 
correct in taking 60 as fairly representing the chromosomes in the prothal- 
lium. But with the embryo it is different. We find our numbers fall into 
two discontinuous groups, one ranged closely about 60 (59-64) the other 
approximating to 78 (77-80). Similarly, in respect of Scolopendrium 
vulgare var. crispum Drnmmondae , whilst the prothallial countings gave 
70-75 as an average number, it was clear that the embryo contained more, 
ranging perhaps from 95-105, or say 100, as a mean. These indications 
of individual differences are of interest when taken in connexion with the 
varietal differences. For, along with much evidence — which conveying from 
many sources seems to testify to the permanence of the chromosomes — 
we meet notwithstanding with positive cases of chromosome fluctuation 
that might seem to negative any value being attached to number. 
Even in other plants and animals, in which the numbers are low, 
we find differences in closely allied species which are difficult to account 
for, although they prove that the fractionation of the linin that bears the 
chromatin is subject to change, introduced either through rearrangement 
of the primoridia, or owing to the limits between individual chromosomes 
losing their original precision. And if, as we have strong grounds for 
believing, the chromosomes are intimately associated with hereditary 
qualities of the organism, it is evident that a disturbance of the chromosome 
structure would, ceteris paribus, be likely to be associated with variation. 
But it is evident that one must keep distinct two kinds of chromosomic 
differences. In the ordinary somatic mitoses the entire nuclear linin 
and chromatin is equally halved between the two daughter nuclei, and 
for this purpose it is difficult to see how the mere chance of any temporary 
end-to-end adherence — or even an increased fractionation— of the individual 
chromosomes could affect the final result. But in meiosis, where there 
is a segregation and ultimately a distribution of units contributed by the 
paternal and maternal ancestors respectively, it is readily comprehensible 
that any such destruction of the individuality of the chromosomes might 
find expression in the production of sports, or unlooked-for variations. 
Regarding the instances of apogamy and apospory which have been 
described in this paper from the point of view of their nuclear history, 
it is clear that there are two main groups into which they severally fall. 
Firstly, we have forms in which fertile spores are produced in connexion 
with the ordinary process of meiosis. To this category the two varieties 
polyddctyla of the common Male Fern belong. Secondly, there are those 
