320 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



" moderate " susceptibility, so that the presence of factors checking 

 the intensity of susceptibility has to be recognized. 



Further, crosses made between " slightly " and " moderately " 

 susceptible varieties often give, in the generation raised from the 

 hybrid, forms far more susceptible than the " moderate " parent. 

 This is particularly the case in crosses between ' Rivet ' wheat (slightly) 

 and ' Red Fife ' (moderately susceptible), where forms excessively 

 susceptible to yellow rust appear in the generation raised from the 

 hybrid. These in turn may breed true to this feature. The statistical 

 investigation of the phenomena is a matter of considerable importance, 

 but unfortunately it is proving difficult, owing to the partial sterility 

 of many of these new forms. Strikingly enough, with this increased 

 susceptibility to a disease to which one at least of the parents is liable, 

 one may find susceptibility to other diseases not known to occur in 

 them. The production of races of wheat readily attacked by ergot 

 from the cross between ' Rivet ' and ' Red Fife ' is a case in point.* 

 The fact that such may occur is, however, a small matter to set against 

 the undoubted advantages of breeding directly for disease-resistance. 

 The recognition of the fact that immunity and susceptibility to certain 

 diseases are capable of segregation in either a simple or complex 

 Mendelian fashion has led to a great effort to control some of the 

 commoner diseases to which our crops are liable, and breeding for 

 disease-resistance has become part of the routine work of many ex- 

 perimental plant-breeding stations. Results in this direction cannot, 

 from the nature of the work, be expected rapidly, though some of 

 considerable economic significance are already to hand. Meanwhile 

 the way for further progress might well be paved by those Horti- 

 cultural and Agricultural Institutions which make trials of large 

 numbers of varieties of the more important garden and farm plants, 

 collecting information with regard to their susceptibility or otherwise 

 to various diseases. 



The Chairman said that he had been particularly interested in 

 Professor Biffen's remarks, in the earlier part of his lecture, suggesting 

 that the increased feeding of plants seemed to render them more 

 susceptible to disease, and thought that it indicated that what is now 

 popularly known as " intensive cultivation " might soon be on its 

 trial for the reason stated in the lecture. He also thought that 

 growers might themselves exert great influence in stamping out 

 disease by insisting on receiving for their cultivation only varieties 

 which are immune, or practically immune, from those forms of disease 

 to which the species concerned are more commonly subject. 



Mr. Bateson asked whether there was any truth in the popular 

 view that disease-resistance was probably associated with " inferiority." 

 Varieties might of course be inferior in many distinct ways, but perhaps 

 small size and a deficiency of sugars or of aromatic substances were 

 the most usual elements of inferiority in edible plants. Did Professor 



* Eiffen, R. H., Journ. Agric. Sci. vol. iv. p. 426. 



