THE WHITE BLACKBERRY 885 



Why, then, you ask, has not natural selection 

 developed a race of white blackberries? 



I am not sure that anyone can give an ade- 

 quate answer. Perhaps it is desirable to have 

 the seeds of a plant protected from the rays of 

 the sun, particularly from those ultra-violet rays 

 which are known to have great power in produc- 

 ing chemical changes. Recent studies of the 

 short waves of light beyond the violet end of the 

 spectrum show that they have strong germicidal 

 power. 



It will be recalled that the celebrated Danish 

 physician Dr. Finsen developed a treatment of 

 local tubercular affections based on the principle 

 that ultra-violet light destroys the disease germs. 

 And most readers have heard of Dr. Wood- 

 ward's theory that very bright hght is detri- 

 mental to all living organisms. 



Possibly too much sunlight might have a dele- 

 terious effect on the seeds of such a plant as the 

 blackberry. Indeed, the fact that the berry 

 quickly develops pigments under ordinary con- 

 ditions, and develops them much earlier than the 

 stage at which it is desirable to have the fruit 

 eaten by birds, suggests that this pigment is 

 protective to the fruit itself in addition to its 

 function of making the fruit attractive to the 

 bird. 



