1915] East,— Dr. Gates’s Mutation Factor in Evolution 237 
reduce to four: (1) It has been definitely proven that O. Lamarckiana 
is not a hybrid; (2) Constant ratios of the usual Mendelian type are 
not found; (3) Splitting often occurs in the F; instead of the F, genera- 
tions, sometimes with the production of two types unlike the parents 
(twin hybrids); and, (4) Chromosome differences appear. 
In regard to the first point, it may be said that the finding of a 
single herbarium specimen hardly constitutes proof that the plant in 
question is or is not a hybrid The second point is covered by our 
remarks on the selective elimination of zygotes and gametes. The 
third argument overlooks a fundamental tenet of Mendelism. Crosses 
split first in the second hybrid generation, solely when the eggs on 
the one hand and the sperms on the other hand entering into the so- 
called F; generation were of the same factorial constitution. The mere 
act of producing a cross does not necessarily make the next generation 
an F; generation. The fact that O. Lamarckiana gives off variants is 
to many an indication that a cross between it and another form does 
not produce an F, hybrid. The frequency or infrequeney with which 
the aberrant types appear proves nothing as long as we are ignorant 
of the potentalities of the non-functional gametes and zygotes. With 
this ignorance to contend with, the variability of the ratios is even an 
argument in favor of segregation rather than mutation, for it must be 
remembered that the same types continually reappear, whereas by 
DeVriesian theory mutations are equally likely to occur in any direc- 
tion. The fourth argument of the author is really a question of termi- 
nology. If the behavior of the chromosomes is the efficient cause of 
Mendelian phenomena, then even aberrant mitoses at reduction are 
in the broad sense Mendelian. They hold possibilities of variation 
without that true germinal change which may be pictured as a chemical 
reconstitution independent of the mechanics of cell division. 
In calling attention to these points, however, the reviewer does not 
wish to have it understood that he denies mutation. Wide variations 
and narrow variations as opposed to mere adaptive fluctuations cer- 
tainly appear, and some of these variants may have been produced 
independently of “slips” in cell division. But it seems to him unwise 
to make the case rest upon the Oenothera data. The author speaks 
truly when he says that "biology has passed the stage when single 
evolutionary factors, no matter how insistently urged or how bril- 
liantly advocated, can be held accountable for the great diversity of 
life which we see around us." — E. M. Easr. 
