THE MUTATION THEORY 355 
biennial culture for the other. Rubrinervis may be annual in appar- 
ently all specimens, in sunny seasons, which would allow a large 
part of the gigas to remain in the state of rosettes during the entire 
first summer. It would be very interesting to obtain a fuller insight 
into the relation of the length of life to other qualities, but as yet 
the facts can only be detailed as they stand. 
Both of these stout species have been found quite constant from 
the very first moment of their appearance. I have cultivated them 
from seed in large numbers, and they have never reverted to the 
lamarckiana. From this they have inherited the mutability or the 
capacity of producing in their turn new mutants. But they seem to 
have done so incompletely, changing in the direction of more absolute 
constancy. This was especially observed in the case of rubrinervis, 
which is not of such rare occurrence as O. gigas, and which it has been 
possible to study in large numbers of individuals. So for instance, 
“the red-veins” have never produced any dwarfs, notwithstanding 
they are produced very often by the parent-type. And in crossing 
experiments the red-veins gave proof of the absence of a mutative 
capacity for their production. 
[Besides the mutants just described there occurred two weak forms 
that could survive only if reared under protection and would have 
failed to survive in nature. Here we have a place for the action of 
natural selection, but operating with mutations instead of with 
fluctuating variations. These two mutants are “the whitish and the 
oblong-leaved evening-primroses or the Oenothera albida and oblonga.” 
All of the mutants so far mentioned are constant forms that breed 
true to type. Certain other types were either incapable of being bred 
or else were decidedly inconstant. O¢enothera lata had only pistillate 
flowers and therefore could not be fertilized by pollen of the same 
mutant. Odcnothera scintillous and O. elliptica are fertile to their own 
pollen, but produce progeny only partly like the parent, the rest 
reverting to the original type Oenothera lamarckiana.—Eb.] 
SUMMARY OF DE VRIES’S MUTATION THEORY’ 
THOMAS HUNT MORGAN 
We may now proceed to examine the evidence from which De 
Vries has been led to the general conclusions given in the preceding 
pages. De Vries found at Hilversum, near Amsterdam, a locality 
tT. H. Morgan, Evolution and Adaptation (1903). Used by special permission 
of the publishers, The Macmillan Company. 
