212 Retrograde Varieties 



cies will continue during a number of years, 

 and it may not be possible to get rid of them 

 at all. 



It is an often recurring assertion that white 

 varieties of colored species are the most stable 

 of all horticultural races. They are often said 

 to be at least as constant as the species itself, 

 and even to surpass it in this quality. With our 

 present state of knowledge, the explanation of 

 this general experience is easily given. For se- 

 lection removes the effect of spontaneous cross- 

 es from the variety in each year, and renders it 

 practically pure, while it is wholly inadequate 

 to produce the same effects on the species, be- 

 cause of the concealed hybrids. 



The explanation given in this simple instance 

 may be applied to the case of different varieties 

 of the same species, when growing together 

 and crossed naturally by insects. 



It would take too long to go into all the de- 

 tails that present themselves here to the stu- 

 dent of nature and of gardens. I will 

 only state, that since varieties differ princi- 

 pally from their species by the lack of some 

 sharp character, one variety may be character- 

 ized by the lack of color of the flowers, another 

 by the lack of pubescence, a third by being 

 dwarfed, and so on. Every character must be 

 studied separately in its effects on the offspring 



