330 Origin of Each Species Considered Separately. 



as one unit to external stimuli, and also that in hybridi- 

 zation and other breeding experiments these characters 

 behave as if combined into inseparable groups.^ 



If we should ultimately succeed in splitting up the 

 group of riihrinervis-z\'\2ir2iQ.tQvs into its component units 

 we should of course demonstrate its compound nature. 

 But until this has been done it seems to me both simpler, 

 and better in accord with the facts, to adopt the view 

 that the sum total of the characters is the expression of 

 a single elementary "unit." 



How it comes about that this ''unit" can make the 

 walls of the bast-fibres thin, the leaves narrow and gray- 

 green, the veins and fruits reddish, is a question which 

 cannot be answered at present. But chemical combina- 

 tions also possess many attributes the interdependence 

 of which one is far from being always able to explain. 



I shall not go further into this question now ; but 

 before I leave it I wish to insist on the fact that the 

 whole so-called ''habit" of a species can be so much 

 altered by a mutation that, during its whole life and in 

 every organ it differs from the species from which it 

 arose. 



If we refer to the pedigrees and tables of mutations 

 given in sections 1-8 we shall find the cases of O. rubri- 

 nerz'is which are recorded in the following table. In it 

 we see that one 0. rithrinervis occurs in about every 

 1000 seedlings. 



Besides this, O. ruhrinervis arose twelve times in 

 other cultures which were either lateral branches of the 

 pedigrees referred to, or had arisen from crosses. I have 

 summarized these in Table II. 



The proportion of 0. ruhrinervis to the whole num- 



^ Intracellulore Pangenesis, pp. 21, 33, ec. • 



\ 



