Applicalion of Biological Principles to Plant Breeding 127 



Recently, accurately controlled in\-estigations have 

 shown that a strict jNIendelian notation will inteq^ret results 

 that hitherto had been given the name blended inheritance. 

 For instance, one may cross an eggplant, Solamim mclon- 

 gena, bearing large fruits with one bearing small fruits. 

 In the first hybrid generation, fruits intermediate in size are 

 produced. Segregation in the second hybrid generation is 

 such that plants bearing fruit like either parent can be 

 obtained if a large number of individuals (several thousand) 

 are grown. Yet among the F^ progeny, intermediates still 

 occur in large numbers, and from them pure t^pes can be 

 secured. 



Most of the characters hitherto described are qualitative 

 in nature. They are either present or absent in the differ- 

 ent varieties. Such characters are generally dominant, 

 in which case the heterozygotes are like the homozygotes 

 in appearance. Other characters give heterozygotes inter- 

 mediate in appearance, owing to incomplete dominance, 

 but these intermediates can never be fi.xed. Owing to their 

 heterozygous constitution they always segregate the paren- 

 tal characters in the next generation. Size characters or 

 ciuantitative characters, on the other hand, are often xery 

 complex. They are due to the interaction of mam- factors. 

 For this reason blends may be obtained in the F, genera- 

 tion that are homozygous for such a combination of game- 

 tic factors that they always breed true to that condition 



(Fig. 55)- 



Fortunately it is not necessary always to have plants 

 that breed true to seed. Many commercial plants are 

 propagated asexually by bulbs, tubers, cuttings, etc. 

 Here one has a method of growing portions of a single plant 

 for an indetrnitc length of time. fVuit trees, bush fruits, 



