2G GENETICS IN RELATION TO AGRICULTURE 



(6) 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 35C.) and the re- 

 mainder in a cool house (temperature from 15 to 20C.), 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 larvae of bees determines whether the females shall be fertile 

 (queens) or infertile (workers), (Fig. 10). The striking differences in 



FIG. 10. The three forms of bees: a, drone; 6, queen; c, worker. The two latter develop as 

 the result of difference in the food supplied to the larvae. (After Harrison.) 



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 (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 



