318 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
cool temperature the flowers which develop later on will be normal 
red in color. Thus it cannot be said that this primula inherits either 
red or white flowers. What it really inherits is ability to react in 
certain ways under the influence of temperature. 
c) Food and fertility. It is well known that the kind of food 
supplied to the larvae of bees determines whether the females shall be 
fertile (queens) or infertile (workers). The striking differences in 
structure and instincts of the two classes of females are all conditioned 
by the food provided for the larvae. Each larva inherited the capacity 
to react in either way according to the stimulus received. 
d) Moisture and structure. Morgan reports a variety of the 
pomace fly, Drosophila ampelophila, with abnormal abdomen; “the 
normal black bands of the abdomen are broken and irregular or even 
entirely absent. In flies reared on moist food the abnormality is 
extreme; but even in the same culture the flies that continue to 
hatch become less and less abnormal as the culture becomes more 
dry and the food scarce, until finally the flies that emerge later cannot 
be told from normal flies. If the culture is kept well fed (and moist) 
the change does not occur, but if the flies are reared on dry food they 
are normal from the beginning.” 
3- Environment may cause new heritable characters.—As yet 
there is a dearth of evidence which can be accepted as scientific proof 
that external stimuli actually cause germinal variations. At the same 
time there is an abundance of data which falls into the class of circum- 
stantial evidence in favor of such a doctrine. Moreover, there are 
a few cases in which new heritable characters, have been artificially 
produced by carefully controlled external stimuli. Hence some 
germinal variations are apparently caused by known environmental 
conditions and we are justified in recognizing this third category of 
developmental differences due to environmental effects. 
Considerable evidence of permanent changes in both morphologi- 
cal and physiological characters has been secured from experiments 
with the culture of bacteria and yeast, in unusual culture media, in 
the presence of toxic solutions, or under extreme temperature condi- 
tions. The significant results of four investigators who worked 
independently, Hansen, Barber, Wolf, and Jordan, have been reviewed 
and discussed in regard to their bearing on genetic theory by Cole 
and Wright. The four investigators mentioned above used refined 
methods and three of them began by isolating a single organism from 
whose progeny they obtained distinct strains or biotypes which 
