148 Retrograde Varieties 



group of negative variations, as we have defined 

 them. But the same thing occurs also with 

 positive varieties, though of course, such cases 

 are very rare. The best known instance is that 

 of the ever-flowering begonia, Begonia semper- 

 florens, which has green leaves and white flow- 

 ers, but which has produced garden varieties 

 with a brown foliage and pink flowers. Here 

 also the new quality manifests itself in different 

 organs. 



Enough has now been said on correlative 

 changes, to convince us that they are as a rule 

 to be considered as the expression of some gen- 

 eral internal or physiologic quality, which is not 

 limited to a single organ, but affects all parts 

 of the organism, provided they are capable of 

 undergoing the change. Such characters are 

 therefore to be considered as units, and should 

 be referred to the group of single characters. 



Opposed to these are the true compound char- 

 acters, which consist of different units. These 

 may be segregated by the production of varie- 

 ties, and thereby betray the separate factors of 

 the complex group. 



The most beautiful instances of such complex 

 characters are offered by the colors of some of 

 the most prized garden-flowers. Barely these 

 are of a single hue, often two or three shades 

 contribute to the effect, and in some cases spe- 



