ApriL 19, 1912] 
of variations in the direction of better fit- 
ting the organism to its environment. 
Lamarek and his followers have strongly 
maintained this hypothesis and many scien- 
tists even to-day believe in the effectiveness 
of environment in developing adaptive 
changes. Breeders have carried this prin- 
ciple so far as frequently to advocate the 
erowing of plants in the environment most 
likely to produce the change desired, as, for 
instanee, cultivating tall plants like twi- 
ning beans in the north or at high altitudes 
if it is desired to produce a dwarf type or, 
vice versa, breeding the plants in the south 
and at a low altitude if a giant or tall type 
is desired. Weismann and his school of 
followers have apparently exploded this 
idea by demonstrating that characters ac- 
quired as a result of changed environment 
are merely physiological changes and are 
not inherited. The question, however, is 
by no means settled and we must await fur- 
ther evidence. 
Knight believed that increased food 
supply caused an increase in the range of 
variation and that it was important for 
breeders to manure their plants heavily. 
De Vries, on the contrary, would have us 
believe that such variations are fluctua- 
tions and non-heritable. The studies of 
Weisse, Reinhold, MacLeod, Tammes and 
Love have given us many instances where 
the range of variation is increased as a re- 
sult of food supply and other instances 
where the variation is apparently greater 
on poor or sterile soil. 
It would seem that any treatment that 
would increase the range of variation, in 
plants that are grown for breeding pur- 
poses would be valuable, but it still remains 
to be definitely proved whether such in- 
creases in the range of variation are in any 
marked degree heritable and whether valu- 
able maximum variates can be more fre- 
quently produced in this way than would 
SCIENCE 
605 
be found in similar groups of plants under 
ordinary treatment. 
It is only very recently that the idea has 
developed that we can go farther than pos- 
sibly change the environment. With the 
publication of MacDougal’s researches in 
1906 describing mutations that were ap- 
parently caused by injecting the capsules 
of plants with certain solutions, such as 
zine sulphate, magnesium chloride and the 
like, a possible new method of forcing 
variations was introduced. MacDougal 
apparently obtained marked variations as 
a result of his treatment, which were in- 
herited in succeeding generations. 
Tower, by subjecting potato beetles dur- 
ing the formation of the germ cells to ex- 
tremely hot and dry or hot and humid 
conditions with changes of atmospheric 
pressure, was able to cause the development 
of marked changes or mutations which 
were found to transmit their characters 
true through several generations and 
which segregated as unit characters follow- 
ing hybridization. He concludes from his 
experiments ‘‘ that heritable variations are 
produced as the direct response to external 
stimuli.’”’ 
Gager has produced similar changes in 
plants by subjecting the developing ova- 
ries of plants to the action of radium rays 
and a number of similar studies by Hert- 
wig and others indicate that radium ema- 
nations have a very active effect on both 
plants and animals. 
While the evidence favoring the value of 
such external stimuli as the above in pro- 
ducing new heritable characters is appar- 
ently definite and positive, the extent to 
which the method can be used in practical 
breeding has not been determined, and in- 
deed we must await further evidence be- 
fore we can finally accept the evidence, or 
the interpretation of the evidence, pre- 
sented in these very valuable and suggest- 
