Increase in Variability in One Direction. 9 



cies. In cases where the origin of such a novelty is satis- 

 factorily known it always happened suddenly. For the 

 combination of several characters in the same variety 

 see Vol. I, p. 197. 



2. On the oilier hand some horticultural varieties are 

 compound types zvhich owe their existence to the associa- 

 tion of two {or more) antagonistic characters. The two 

 characters tend to exclude one another more or less com- 

 pletely and struggle for the upper hand ; from this there 

 results a very high degree of variability in their mani- 

 festation (as in variegation, stripes, doubleness and so 

 forth). These forms usually first appear as minus var- 

 iants, i. e., with a slight degree of development of the 

 abnormality in which condition they are sought for and 

 isolated and subsequently improved by selection. The 

 artificial production, therefore, of such a form is not a 

 sudden one but a process of gradual improvement. Their 

 first origin however remains unknown. 



§2. THE DOCTRINE OF THE INCREASE IN VARIABILITY 



IN ONE DIRECTION BROUGHT ABOUT 



BY SELECTION. 



One of the most attractive parts of the doctrine of 

 selection is that according to which variability may be 

 increased by selection. Many observations, especially in 

 horticulture, seem to support this view ; which, if it were 

 true would afford an almost irrefutable argument in favor 

 of the prevailing belief in the omnipotence of natural 

 selection fVol. I, p. 119). 



Varieties are said to be incipient species. Bv selecting 

 the individuals which deviate most from the type of the 

 species it is believed to be possible to attain first to varia- 

 tions and then to varieties. To these is ascribed the 



