246 



Rust in Wheat. 



[JULY, 



the man who has to grow the crop at a profit. An example 

 of such a case is provided by the Evergood potato ; it is very 

 resistant to the attacks of potato disease, yet it shows no signs 

 of supplanting the exceedingly susceptible Up-to-Date, chiefly 

 because of the indifferent quality of the tubers. 



The possibility then has to be considered whether this 

 feature of disease resistance, when found, can be combined 

 with other good features by crossbreeding. Until the opening 

 years of this century there was little chance of accomplishing 

 this owing to the fact that our knowledge of plant breeding 

 was too slight. Still many breeders had set themselves the 

 task of raising disease-resisting plants of various kinds, and 

 it is curious to note how confident breeders have always been 

 that they would succeed in the long run. Their opinion was 

 based upon the fact that the descendants of a hybrid plant 

 were frequently very unlike the parents and one another. 

 Many of these were obviously useless, yet some few might 

 show improvements on the plants used as the parents of the 

 hybrid. Amongst them they hoped to find some showing the 

 feature of disease resistance. The finding of the required 

 type was thus a matter of chance, but so fascinating is the 

 subject that men have been found to spend the greater part 

 of their days working on in the hope that success would come 

 in the near future. 



Within the last few years, the problems of breeding have 

 been investigated in great detail, and it is now known that 

 certain definite laws underlie the phenomena which, till recently, 

 appeared hopelessly complex. The " breaking of the type," 

 seen when the descendants of the hybrid were raised, is now 

 seen to be so simple a matter that in many cases it is possible 

 to predict with extraordinary accuracy not only just what 

 types will appear but even the numbers of them. 



The laws discovered by Mendel have been confirmed time 

 after time, and they are now 7 recognised as being of very 

 general application. As a direct result of a knowledge of them 

 a definite system has been introduced into breeding, and now 

 instead of blindly crossing varieties in the hope of obtaining 

 a desired " break," the breeder can make his choice of plants 

 knowing that he can combine the features occurring in them 

 in anv fashion he wishes and further obtain his new varieties 



