30 HEREDITY AND THE ORIGIN OF SPECIES. 
known. This single aberrant individual might have been 
a mutant of low frequency, comparable to gigas derived 
from Lamarckiana, and its recurrence here might have 
been merely a matter of chance. However, in another spe- 
cies of evening - primrose, Raimannia odorata, a flower 
which belongs to a separate genus of the family, and is not 
known to be mutating, the treatment described resulted 
in a large number of aberrant individuals of a hitherto 
unknown type. Some of these, which show a shorter life- 
cycle than the parental form, and many anatomical diver- 
gencies, have been brought to bloom and to maturity, and 
the new form is obviously a potential species. In this ex- 
perience, exemplified by specimens of the normal, parental 
forms, and aberrant mutants, I am able to offer you con- 
clusive proof that agencies external to the cell may in- 
duce mutations, and consequently exert a profound in- 
fluence on heredity. It would not be well to exaggerate 
the importance of this result, yet it is evident that the 
establishment of this fact marks a long step forward in 
the experimental study of inheritance and the origin of 
species. , 
A brief summary of the foregoing discussion may be 
made in the following generalizations: 
I. Species may arise by hybridizations which result in 
fixed forms. A large number of forms known as species 
and recognized to be of such origin are known and a num- 
ber of them have been duplicated in experimental cultures, 
some of which were made over a half century ago. 
2. The mutation theory groups an enormous number of 
hitherto unexplainable facts, to which we are constantly 
adding in great volume, into a connected and meaningful 
whole, and best of all it brings the subject anew into a 
condition where it is amenable to experimental methods, 
in the laboratory, and experimental garden. 
3. As a result of the theoretical conceptions offered us, 
