LUTHER BURBANK 



culty is to prevent crosses that are not desired. If 

 the plants are shielded from the visits of the bees, 

 and careful hand pollenizing is effected, there is 

 no great difficulty in combining the different forms 

 in such a way as to get definite results, and the 

 hybrid forms may be fixed by careful selective 

 breeding. 



Of course, when you deal with a spurless form, 

 if the individuals that you use are themselves 

 hybrids of the first generation of a cross between 

 a spurred and a spurless variety, their progeny, 

 when they are crossed with a spurred variety, will 

 be in effect second generation hybrids and only 

 half of them will be spurless. But this, again, 

 merely illustrates the familiar segregation of char- 

 acters and the reappearance of the recessive trait 

 in this case the spurred condition in a rather 

 definite proportion of the second generation 

 progeny. 



Another anomaly among the columbines that 

 offers good opportunity for experimental tests is 

 furnished by the double varieties. I used to notice 

 that if you crossed a double and a single one, you 

 are about as likely to get a double as a single. 

 Here, again, it would appear that the double con- 

 dition of corolla acts as a Mendelian dominant 

 factor, and that the strains with which I worked 

 were themselves mixed. 



[54] 



