546 Lewis . — The Behaviour of the Chromosomes 
Briefly then the theory of the individuality of the chromosomes finds 
its strongest support in the behaviour of the chromosomes in hybrid forms, 
coupled with the presence of the peculiar differentials and the observed 
methods of separation and distribution during the two divisions attending 
reduction. Conclusive as the evidence in favour of the hypothesis seems 
to be, the recent contributions of Foot and Strobell (’07), Farmer (’07), and 
of Mottier (’07), have strongly questioned its validity. These writers have 
pointed out certain objections to the hypothesis, chief among which may 
be mentioned the difference in the number of chromosomes typical of 
a species, and the number of characters into which the specie's may be 
analysed which behave as distinct allelomorphs. This objection was also 
recognized by Weismann, but has been given new meaning through the 
definite proof afforded by recent experimental work. It has been urged 
that each chromosome may be regarded as a material primordium for 
a group of correlated characters, and this is to a certain extent borne out 
by experimental evidence. For example, Mendel (’65) found that in Pisum 
a grey, grey-brown, or leather-brown colour of the seed-coat always occurs 
in connexion with violet-red blossoms and reddish spots in the leaf-axils. 
This correlation of all the characters in groups becomes lost, however, 
when the entire number and relative independence of the allelomorphs is 
considered. It seems necessary to associate some smaller unit with the 
occurence of unit characters. 
Brauer (’93) thought that the chromomere rather than the chromosome 
should be regarded as the element which retains its individuality from cell 
generation to generation. This theory has recently received new recog- 
nition from Mottier (’07) and later from Farmer (’07). Mottier has 
suggested that the smallest visible chromatin granule be taken as the 
unit which retains its individuality. These units he designates as pangens. 
The next higher aggregation of granules is the chromomere. Farmer (’07) 
regards the chromomere as the distinct entity and material primordium 
of the unit characters. He considers the chromosome as made up of 
a number of organized chromomeres, but the same chromomeres do not 
necessarily always go together to form a chromosome. There is, therefore, 
according to this view no persistence of the chromosomes from cell genera- 
tion to generation as distinct individuals, but rather they are formed anew 
at each succeeding division out of the individual chromomeres which have 
retained their identity. 
Much importance has always been attached to the fact that the 
chromosomes are constant in number, and much speculation has been 
based on the number of chromosomes in the germ-cells of certain species. 
Farmer (’07) has shown that in certain ferns chromosome numbers are 
present which deviate greatly from the number typical of the species from 
which they have sprung. He concludes that this number must have arisen 
