82 



PLANT-BREEDING 



have the effect of rapidly increasing the number of types, 

 even if ordinary mutability is slow in producing new units. 

 For, by tliis crossing, each new unit will become united 



Fig. 23. Stiff -branched Svalof oats. 



with many of the existing types and, in the end, perhaps, 

 with all of them. In this way, the production of one really 

 new unit will tend to double the number of the existing 

 types, and, in the cases of many garden flowers, where such 



