VARIATION AND DISEASE. 177 



over that the question of breeding disease-proof 

 varieties of our cultivated plants is complicated by 

 the danger of our breeding at the same time 

 adapted races of their pests. It appears at first 

 sight extremely improbable that we should escape 

 the danger by breeding from those specimens of 

 our plants which have best survived a fungus 

 epidemic. Still, it must not be forgotten that 

 " hardy varieties," and races adapted to other 

 exigencies of the non-living environment, have 

 been bred by selection and nevertheless this 

 variable non-living environment is always with us. 

 The matter is therefore simply and solely one of 

 experiment, and the retort that a disease-resisting 

 variety of any particular plant has not yet been 

 raised is no more valid than the objection that a true 

 blue primrose has not yet been obtained: whether 

 the same remark can be made with regard to any 

 hope of a disease-proof plant may be another 

 matter, but in any case it must be made more 

 cautiously in the light of our present experience. 



Notes to Chapter XVIII. 



The reader will find more on this subject in Bailey's 

 Survival of the Unlike and the literature quoted in the notes 

 to Chapter VIII. 



For varieties of Indian Wheats, etc., see Watt, Agricultural 

 Ledger, Calcutta, 1895. 



For a discussion on so-called " Disease-proof Wheats " 

 consult Eriksson & Henning, Die Getreideroste. 



Magnus' paper is in the BericJite der Deutscken dot. 



GescllscJi., 1894, p. 39. 



M 



