156 SYSTEMATIZED PLANT-BREEDING 



starting point in the form of varieties resistant 

 to any special disease could at will transfer this 

 immunity to other varieties and so play a part in 

 its control. It is too early to say how far these 

 results will hold with regard to other diseases but 

 in two other cases which have been tested fairly 

 thoroughly, namely a mildew on barley and a 

 second rust on wheat, similar results have been 

 obtained. 



The next step was to arrange a demonstration 

 of the facts for our critical friends the farmers. 

 This took the form of small plots one yard square 

 sown wth four types isolated from the cultures 

 of the previous year. Two'of the types resembled 

 the parents, one having the dense ears of American 

 Club and its rust resistance, the other the lax ears 

 of Michigan Bronze and its extreme susceptibility 

 to disease. The other two showed resistance in 

 association with lax ears and susceptibility with 

 dense ears, or to put the matter more simply they 

 were immune forms of Michigan Bronze and suscep- 

 tible forms of American Club. The plots were 

 arranged draught-board fashion with the resistant 

 and susceptible forms alternating in each row of 

 squares. During the summer months the regular 

 patchwork of orange and green formed a striking 

 demonstration of the possibility of definitely 

 breeding for rust resistance. At harvest too they 

 gave some idea of the losses which a severe epidemic 

 can cause, for whilst the resistant plots produced 



