PLANT BREEDING. 157 



cross between Diana-Hamburg and a seedling of Concord. 

 The method of using what Webber has called " dilute hybrids " 

 has also been employed with success, p^articularly in the fixa- 

 tion of types. 



THE LIMITS OE CROSSING. 



" Crossing is useful as a means of originating new forms 

 adapted to man's special uses and also as a means of revitalizing 

 the offspring by providing new combinations of characters 

 which may better enable the individual to compete in the strug- 

 gle for existence ; but there are limits beyond which crossing is 

 useful neither to the species nor to man." $ 



Without discussing this subject at length, it may be said that, 

 within certain limits, the wider the divergence of the parents in 

 any fertile cross, the more vigorous the progeny. This state- 

 ment rests on the broad basis of fact, and is corroborated by the 

 work of Darwin and others down to the present day. Nature 

 has comparatively few varieties, the initial variation being 

 usually crowded out in the fierce struggle for existence; but 

 among cultivated plants instead of struggle for existence and 

 the survival of the strongest, we have a struggle for improve- 

 ment and a " survival of the most coveted." Weeds are best 

 fitted to survive, but the hoe and the cultivator enable the 

 weaker and, for man, the more desirable species to prevail. 



So then cultivated plants, leading a life of comparative peace, 

 expend their energies along the lines which are laid down by 

 man. Variations appear and are carefully watched, guarded, 

 and propagated ; with the result that in time a new type or 

 variety is produced. But the conditions are vastly more varia- 

 ble than are those under which their wild allies are growing. 

 This leads to a wide range of characteristics found in the same 

 variety, consequently unions are here more powerful than in the 

 wild state, and the expert plant breeder is he who manipulates 

 these forces and their combinations to the best advantage. In 

 the past history of plant breeding this manipulation has neces- 

 sarily been carried on more or less blindly, but the work of 

 Mendel, DeVries and others seems to open wonderful possi- 

 bilities in this direction. 



$ Bailey, Philosophy of Crossing Plants. 



