240 Retrograde Varieties 



age of many other plants behaves likewise, as 

 also do apples and peaches on the insolated 

 sides of the fruits. It is quite impossible to 

 state these groups of facts in a more simple way 

 than hj the statement that the tendency to be- 

 7 come red is almost generally present, though 

 latent, in leaves and stems, and that it comes 

 into activity whenever a stimulus provokes it. 



Now it must be granted that the energizing 

 of such a propensity under ordinary circum- 

 stances is quite another thing from the orig- 

 ination of a positive variety by the evolution 

 of the same character. In the variety the ac- 

 tivity has become independent of outer in- 

 fluences or dependent upon them in a far lesser 

 degree. The power of producing the red pig- 

 ments is shown to be latent by the facts given 

 above, and we see that in the varietv it is no 

 longer latent but is in perfect and lasting ac- 

 tivity throughout the whole life of the plant. 



Red varieties of white flowers are much more 

 rare. Here the latency of the red pigment may 

 be deduced partly from general arguments like 

 those just given, partly from the special syste- 

 matic relations in the given cases. Hildebrand 

 has clearly worked out this mode of proof. He 

 showed by the critical examination of a large 

 number of instances that the occurrence of the 

 red flowered varieties is contingent upon the 



