206 



PLANT HYBRIDIZATION BEFORE MENDEL 



as in sexual capacity^ are hybrids for the most part distinguished 

 from the two parental species. 



Crosses between different races and species are distinguished 

 from individuals of a pure race by their vegetative activity. 



Hybrids between markedly different races, he remarks, are fre- 

 quently very tender, especially in youth, so that the rearing of the 

 seedlings takes place with difficulty. Hybrids between more nearly 

 related species and races^ on the other hand^ are as a rule thrifty 

 and vigorous; they are distinguished for the most part by size, 

 rapidity of growth, early flowering, abundance of bloom, long 

 duration of life, marked capacity of reproduction, unusual size of 

 individual organs and similar characteristics. 



"Complete reversions to the parental types, without the operation of 

 the pollen of the parents, occur only in the case of the hybrids of nearly 

 related races." 



Focke's own experiments were made in the crossing of species 

 of Raphanus, Melandryum, Rubus, Anagallis, Digitalis, and Nico- 

 tiana. While the actual number of crosses made by Focke was 

 few, and the results, as in the case of most other observers of 

 hybrid phenomena, were not analyzed in respect to the generations 

 of the hybrids, yet in the one case of a cross made between Digi- 

 talis purpurea X ^« ambigua Focke made measurements of cer- 

 tain organs in the parents and in the hybrids, which, so far as 

 the writer's inquiry has extended, with the exception of those of 



Summary of Averages 



Average of length measurements, assuming a mean 



condition to be the normal 

 Average of width measurements 



Theoretical Found 



mm. 



26.3 

 9-6 



mm. 



23.0 



7.0 



