14 



The Plant World. 



the hybrid individuals, the actual ratio of dominants to recess- 

 ives being 5.5:1. While the proportion of recessives is low, the 

 complete dominance of absence of neck in the Fj generation and 

 the subsequent segregation of the unit characters in the follow- 

 ing generation leads us to conclude that we are dealing with a 

 simple Mendelian monohybrid. Twelve other pairs of unit 

 characters gave similar results in the first generation of hybrids, 

 eleven of which segregate in the following generation in accord- 

 ance (approximately) with the Mendelian formula. The other 

 two pairs of characters are known to have shown segregation 

 in the F 2 generation but numerical results were not obtained. 

 The results secured for these various crosses are set forth in the 

 accompanying table. 



It will be seen that in general the results are uniform and 

 consistent except for the last cross which gave two types in the 

 Fj generation, each of which again split in the F 2 generation. 

 The numerical results for this cross are too small to warrant 

 conclusions as to its true nature. 



INHERITANCE OF CHARACTER UNITS IN POL YHYB RIDS. 



In the study of inheritance for other plants it has usually- 

 been found that the unit characters which go to make up the 

 individual are independently heritable. This renders Mendelian 

 inheritance for polyhybrids not only of extreme theoretical 

 interest but enables the plant breeder to secure new and stable 

 combinations by crossing old varieties. 



Coupling of different unit characters appeared in only one 

 cross in our work. This resulted from the cross between Aristo- 

 crat and Burbank's Preserving, in which a complete return to 

 the original parental combinations in the F 2 generation of hybrids 

 was found. The number of plants from this cross was small 

 and the results are not conclusive. 



Purple Flesh and Transparent Skin x Yellow Flesh and Yellow 



Skin. 



In the monohybrid table given above, it will be noted that 

 when a pink and a yellow fruited variety were crossed that there 

 was complete dominance of the pink color in the 1st hybrid 

 generation. In this case the varieties differed only with respect 

 to their flesh color, for both are found to have the same skin 



