26 ‘GENETICS IN RELATION TO AGRICULTURE 
(b) Temperature and Flower Color—Baur reports an experiment with 
a red variety of the Chinese primrose, Primula sinensis rubra. If 
plants of this variety are raised by the usual method until about one 
week before time to bloom and then some of the plants are put in a warm 
room under partial shade (temperature from 30° to 35°C.) and the re- 
mainder in a cool house (temperature from 15° to 20°C.), when they bloom 
those in the warm temperature have pure white flowers while those in the 
cool temperature have the normal red color of the variety. Moreover, 
if plants are brought from the warm into the 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 larvee of bees determines whether the females shall be fertile 
(queens) or infertile (workers), (Fig. 10). The striking differences in 
— —_ 
a b c 
Fia. 10.—The three forms of bees: a, drone; b, queen; c, worker. The twolatter develop as 
the result of difference in the food supplied to the larve. (After Harrison.) 
structure and instincts of the two classes of females are all conditioned 
by the food provided for the larve. 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 (Fig. 60); “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 
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