LUTHER BURBANK 



Perhaps it may be helpful if now, by way of 

 summary, we review in their broader outlines, a 

 few of the principles that have been illustrated by 

 specific cases in the preceding volumes, and offer 

 an added word of explication that may be of aid 

 to the general reader in clarifying his view of com- 

 plex plant hybridizations, and to the plant experi- 

 menter in giving clews that may prove advantage- 

 ous in his work in the field. 



Let us recall, as the text for our first illustra- 

 tion, the simplest case of plant hybridization. 



When, let us say, a thorny and a thornless 

 blackberry are crossed, the offspring are all thorny. 

 But in the next generation a certain proportion of 

 the offspring are thornless. A corresponding case 

 is that of the ordinary blackberry crossed with 

 the white blackberry. All the offspring of the first 

 generation are black, but whiteness reappears 

 among their descendants. 



Let us recall, further, that the process of 

 hybridization consists essentially in bringing the 

 nucleus of the pollen cell in combination with the 

 nucleus of an egg cell. 



Also let us bear in mind a computation that we 

 were able to make with the aid of the physicist, 

 by which we were made aware that the germ cell 

 itself is a highly complex structure with diversi- 

 fied component parts, each of which may be 



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