342 TEE POPULAR SCIENCE MONTHLY 



THE ROLE OF HYBRIDIZATION IN PLANT BREEDING 1 



By Professor E. M. EAST 



HARVARD UNIVERSITY 



THE word hybridization has been used with many meanings. The 

 term is used here to denote the crossing of any two plants that 

 differ from each other in a heritable character, whether they are of the 

 6ame or of different species. 



There is intimate connection between the role of hybridization and 

 the role played by selection. It comes about in this way. Inherited 

 variations are produced by nature with considerable profusion. New 

 characters appear and old characters are lost: these form the working 

 basis of selection. But whether they are large or small they are usually 

 inherited completely. They are the units of heredity; or, if they 

 are sometimes transmitted in units of lesser degree, they may be 

 compared to chemical radicals. 



The main object of hybridization then is the shuffling of these units 

 in the first hybrid generation and their recombination in the next 

 generation. There are, however, various phenomena attending hybridi- 

 zation, and I will endeavor to illustrate the following as those of most 

 importance: (a) Recombination of characters and their fixation, (6) 

 production of desirable combinations in the first hybrid generation and 

 their continuation by asexual propagation, (c) production of fixed first 

 generation hybrids, (d) production of blends. 



If we begin at the real beginning in this discussion, we must say a 

 few words concerning the actual mechanical operations of crossing. 

 The first foundation stone to be laid is a knowledge of the flowering 

 habits and flower structure of the plants to be used. Of course a careful 

 examination of the flowers will show the easiest and surest method of 

 removing the stamens of the flowers that are to be pollinated and of 

 protecting them from foreign pollen. What is not so easily determined 

 are the precise conditions under which the cross should be made to be 

 successful. The proper preparation of the breeding plot even before 

 the plants are grown is necessary. One takes it for granted that some 

 fertilizer will be used, for the plants must be normal to seed well. The 

 three essential elements of soil fertility are nitrogen, potassium and 

 phosphorus, and to get the best results compounds of these elements 

 must be present in proper proportions. First, available potash must be 

 1 This paper is based on one of a series of popular lectures delivered at the 

 Bussey Institution of Harvard University, April and May, 1910. 



