122 Plant-Breeding 



representative species of Europe and Japan; and the 

 same may be found to be true of the common European 

 apple and the wild crab of .the Mississippi Valley. 

 Various crabs of the Soulard type, which were once 

 thought to constitute a distinct species, appear upon 

 further study to be hybrids. We will also recall that 

 the hybrid grapes which have so far proved most 

 valuable are those obtained by Rogers between the 

 American Vitis Labrusca and the European wine grape, 

 Vitis vinifera; and that the attempts of Haskell and 

 others to hybridize associated species of native grapes have 

 given, at best, only indifferent results. To these good 

 results from hybrids and fruit trees and vines, we shall 

 revert presently. 



Variability of hybrids. Another theoretical point 

 which is borne out by practice is the conclusion that, 

 because of the great differences and lack of affinity between 

 parents, pronounced hybrid offsprings are unstable. This 

 is one of the greatest difficulties in the way of the summary 

 production of new varieties by means of hybridization. 

 It would appear, also, that, because of the unlikeness of 

 parents, hybrid offspring must be exceedingly variable; 

 but, as a matter of fact, in many instances the parents are 

 so pronouncedly different that the hybrids represent a 

 distinct type by themselves, or else they approach very 

 nearly to the characters of one of the parents. There are, 

 to be sure, many examples of exceedingly variable hybrid 

 offspring, but they are usually the offspring of variable 

 parents (Fig. 34) . In other words, variability in offspring' 

 appears to follow rather as a result of variability in parents 

 than as a result of mere unlikeness of characters. But 



