SPECIES HYBRIDIZATION 245 



bination of species within the genus, and also of the mutants of 0. 

 lamarckiana with the parent species, with one another, and with other 

 species. 



As an example of the type of behavior displayed by these hybrids we 

 shall take the results of intercrossing lamarckiana and its two mutant 

 derivatives rubrinervis and nanella. When lamarckiana is crossed with 

 rubrinervis, the phenomena are as outlined below: 



lamarckiana X rubrinervis 



lamarckiana subrobusta 



lamarckiana subrobusta rubrinervw 



The F\ consists of two forms in about equal proportions, lamarckiana 

 and subrobusta, the latter a form intermediate between lamarckiana and 

 rubrinervis. In subsequent generations, the lamarckiana individuals 

 breed true, but the subrobusta individuals produce both subrobusta and 

 rubrinervis, the latter breeding true. To these results we may add those 

 obtained by crossing lamarckiana and nanella, the dwarf mutant of 

 lamarckiana. This cross gives in F i approximately equal numbers of 

 lamarckiana and nanella and both forms breed true in subsequent 

 generations. Finally to complete the triangle we may consider the 

 results of hybridization of rubrinervis and nanella which are given below 

 in the form of a diagram. 



nanella X rubrinervis 



lamarckiana subrobusta 



lamarckiana rubrinervis subrobusta dwarfs 



The percentage of subrobusta individuals in the F\ of this cross is usually 

 considerably below 50 per cent. In subsequent generations the subro- 

 busta individuals segregate in the same fashion as those of the FI. The 

 dwarfs obtained in this experiment unite the characters of rubrinervis 

 and nanella and are consequently designated rubrinervis nanella to dis- 

 tinguish them form the true nanella. Like the lamarckiana and rubri- 

 nervis individuals, they breed true in subsequent generations. The actual 

 results of this series of experiments are given in Table XXXIX, from 

 which data on those forms which bred true is omitted. It is at once ap- 



