Chromosomes in Living Organisms. 299 
number of chromosomes may be departed from in the other 
prothallial cells with any possible prejudice to the repro- 
ductive processes, and accordingly the number is found to 
increase, or even to double itself, in the large nuclei of the 
cells forming the walls of the archegonia 1 . 
What has just been stated suffices to prove that variations 
from the determinate number of chromosomes are possible. 
Similar variations have also been observed among animals, 
but I will not discuss them as I am not in a position to 
estimate their significance 2 . Among the examples from the 
plant-kingdom which have been cited, that of the lower 
nucleus in the embryo-sac of the Lilies, so carefully studied 
by Guignard 3 , appears to be the most instructive. This 
nucleus has originally twelve chromosomes, but in the next 
prophase a larger number can be detected. From this it 
might naturally be inferred that the reduction in the number 
of the chromosomes as exhibited in the sexual cells does not 
call for any phylogenetic explanation, and that it is super- 
fluous to regard it as a reversion to an older condition of 
things, since a change in the number of the chromosomes 
may take place quite independently of any such assumption. 
But the variation is essentially different in the two cases. 
The change in the number of the chromosomes which is 
associated with the alternation of generations is accompanied 
by other deep-seated changes, which can be detected in the 
altered appearance of the spore-mother-cells. Moreover the 
change in the number of the chromosomes associated with 
the alternation of generations gives rise, not to a variable, but 
to a perfectly constant result, which can only be attributed to 
phylogenetic causes. The purely vegetative — they may be 
almost called accidental — variations in the number of the 
chromosomes within the limits of any one generation, do not 
otherwise affect the appearance of the nuclei, and the re- 
1 Dixon, loc. cit. , p. 32. 
2 Compare especially Valentin Haecker, Ueb. generative und embryonale 
Mitosen, &c., Arch. f. mikr. Anat., 43, p. 773, 1894. 
3 Loc. cit., p. 187. 
