1914] DE VRIES—OENOTHERA LAMARCKIANA 349 
TRAM” Onno single field was the original form pure; it was always 
mixed to such a degree with O. Tracyi and with their hybrids that 
we found it impossible to collect undoubtedly pure grandiflora 
seed from this locality. Moreover, the intermediate types were 
so numerous (over a dozen) that it was difficult to regard all of them 
as normal hybrids between only two parents. To produce such 
a diversity of forms, either one or both of the parents must have 
een in a mutating condition, or more than two species must have 
combined in the crosses. In both cases, the material can hardly ’ 
be considered as a fit starting-point for experiments bearing upon 
the causal relations of crossing and mutability. 
Recently I have shown that besides O. biennis some other 
species of Oenothera are actually in a state of mutability, and espe- 
cially has one of the most common American types thrown off 
marked mutants in my experiment garden.” The degrees of 
development of this condition, however, are very different in 
different species. In some of them mutations occur rarely, but 
they serve to throw a doubt upon the stability of those forms for 
which no positive results have as yet been won. In other words, 
we may say that almost all the nearest allies of O. Lamarckiana 
are open to the suspicion of sharing at least some degree of the 
mutability of this species. There is no use, therefore, in trying 
to produce mutability by crosses of species of the same subgenus 
(Onagra) in order to show that this phenomenon is only a result 
of crossing, as is asserted by Davis. 
Moreover, I might point out that the question should be dealt 
with from a general standpoint and not be limited to the evening 
Primroses. If it should be true that phenomena like those of O. 
Lamarckiana could be produced by crossing immutable species, it 
would, of course, be of much higher scientific value to produce 
them in other families or genera, or at least in the other subgenera of 
the evening primroses. The chance of finding immutable parents 
for a cross would be far greater and the proof could be given as 
easily and in many cases with less amount of mechanical work 
* DE Vartrs, Hvco, and Barttett, H. H., The evening primroses of Dixie Land- 
ig, Alabama, Science N.S. 35:599-601. 1912. 
* Gruppenweise Artbildung, pp. 296-312. 1913. 
