THE MUTATION THEORY 107 



biennisXmuricata producing one type of Fi and muricataX 

 biennis producing another. Each Fi resembled the father more 

 than the mother. 



2. That each of the hybrids so produced breeds true on self- 

 fertilisation. 



3. That if we speak of the hybrid from biennisXmuricata 

 as BM and of the reciprocal as MB, then 



BMXMB 



gives exclusively offspring of biennis type but that 



MB XBM 



gives exclusively offspring of muricata type. Evidently, apart 

 from all controversy as to the significance of the "mutants" 

 of Lamarckiana, we have here a series of observations of the first 

 importance. 



The fact that reciprocal crossings give constantly distinct 

 results must be taken to indicate that the male and female sides 

 of one, if not of both, of the parents are different in respect of 

 characters which they bear. This is de Vries's view, and he 

 concludes rightly, I think, that the evidence from all the experi- 

 ments shows that both biennis and muricata are in this condition, 

 having one set of characters represented in their pollen-grains 

 and another in their ovules. The plants breed true, but their 

 somatic structures are compounded of the two sets of elements 

 which pass into them from their maternal and paternal sides 

 respectively. This possibility that species may exist of which 

 the males really belong to one form and the females to another, 

 is one which it was evident from the first announcement of the 

 discovery of Mendelian segregation might be found realised in 

 nature. 6 



Oe. biennis and muricata were crossed reciprocally with each 

 other and with a number of other species, and the behaviour of 

 each, when used as mother, was consistently different from its 

 behaviour when used as father. De Vries is evidently justified 



5 In Rep. i to Evol. Committee, 1902, p. 132, attention was called to this pos- 

 sibility, though of course at that date it was in sexual animals alone that it was 

 supposed to exist. It had not occurred to me that even a hermaphrodite plant 

 might be hi this condition. 



