THE CHROMOSOMES 175 
and have larger cells than the type from which they 
may be supposed to have arisen. The most im- 
portant consideration in this connection is that 
since through tetraploidy the number of genes is 
doubled, opportunity is given by further mutation 
in these genes for an indefinite increase in the 
number of genes in the course of evolution. This 
possibility suffices to meet the paradox stated by 
Bateson, that there may have been no increase in 
the number of genes in the course of evolution from 
“amoeba to man.”’ Bateson suggested as a possi- 
bility that all that has happened in the course of 
evolution has resulted from the dropping out of some 
of the original genes. While ‘‘evolution through loss 
of genes”? cannot be refuted as an abstract conten- 
tion, however improbable, it would still leave un- 
solved the whole question as to the origin of the 
genes present ‘at the beginning.” Such a specu- 
lation rests nominally on an hypothesis concerning 
the nature of mutation itself (loss of a factor). 
In a few cases tetraploidy has arisen in pedigreed 
material, and in two cases it has been induced 
artificially. In the evening primrose, Oenothera, a 
tetraploid form occasionally arises. It has been 
called by its discoverer De Vries, O. gigas. The orig- 
inal type O. Lamarckiana has 14 chromosomes and 
O. gigas 28. Stomps has calculated that it occurs 
only once in about 100,000 times. Several possible 
ways in which it arises have been suggested. First, 
that it arises after fertilization through division of 
the chromosomes of the zygote unaccompanied by 
