152 SYSTEMATIZED PLANT-BREEDING 



than is generally realised even amongst the growers 

 themselves. To a certain extent these losses can 

 be avoided, as for instance those caused by the 

 attacks of the smut fungus which can be reduced 

 to a negligible quantity by a preliminary treatment 

 of the grain before sowing. Other fungoid diseases 

 of which the common yellow rust is a conspicuous 

 example are uncontrollable and year by year they 

 take a very appreciable toll of the crop. What this 

 amounts to on the average it is impossible to say 

 at all definitely, but an estimate of from five to 

 ten per cent, is probably not very wide of the 

 real figures. The farmer as a rule pays little atten- 

 tion to its presence, partly because he knows that 

 nothing can be done to prevent it and partly because 

 the attacks never completely cripple the crop in 

 this country. I have even come across cases where 

 the farmer has rather welcomed an attack on the 

 grounds that the leaves died off early and readily 

 separated from the straw during the threshing of 

 the crop. Such ideas would soon disappear if one 

 could but gauge more accurately the part played 

 by each of the various factors determining the 

 yield of the crop. Where for instance a promising 

 plant fails to produce the yield anticipated in the 

 earlier stages of its growth the loss caused by rust 

 is all too often put down vaguely to the weather 

 or to that mysterious blight responsible for most 

 of the crop failures in this and other countries. 

 To any one at all familiar with the losses caused even 



