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 other hand some horticultural varieties are 
compound types which 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 ("Vol. I, p. 119). 
Varieties are said to be incipient species. By 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 
