180 SYMBIOGENESIS 



Prof. Bateson further tells us that though all our finches 

 can breed together, the hybrids are all sterile ; and that among 

 ducks some species can breed together without possessing the 

 slightest sterility, others have totally sterile offspring, and so 

 on. 



In all these instances we have varying degrees of domesti- 

 cation and of induced diathesis which must present a variety of 

 metabolic fluctuations, and, hence, frequent opportunities 

 for the most varying compatibilities, though not necessarily for 

 genuine genetic results. 



It is known that some finches require special " love-foods " 

 (grains) for the production of song, and a progressive 

 in-fertility may thus arise in connection with high aesthetic 

 specialisation alone and the keen discrimination of food that it 

 requires. Ducks, which are far more over-domesticated and 

 also far less engaged in higher kinds of specialisation than 

 finches, may be seen to be far more prone to retrograde fertility. 



That the hybrids produced by the Turnip (Brassica napus] 

 and the Swede (Brassica campestris) are totally sterile is also 

 explainable as arising from over-cultivation, with resultant 

 loss of symbiotics. That they are allied forms does not 

 necessarily imply that their offspring when crossed becomes 

 really " viable." The two strains of the one form when crossed 

 (as in the case of the " rusty" crossed with the healthy wheat) 

 may produce a decided lowering of the resultant, and must thus 

 render heredity which may already have been on its last legs 

 as it were increasingly difficult. This case, therefore, is a 

 confirmation of my remarks on the subject of the miscre of 

 cultivated wheat and the apparent "dominance" of the 

 diseased condition. The expensiveness of the processes of 

 fertilisation and reproduction also has to be taken into account. 

 The cultivated turnip is known to be particularly liable to the 

 attacks of the troublesome Heterodera. The turnip's condition 

 must, therefore, be understood to be pathological and lacking 

 in resistance. In the desert the relation between plant and 

 Nematode is symbiotic and therefore wholesome, and if under 



