7 2o SCIENCE PROGRESS 



a differentiated pair of characters as Mendel himself would 

 have wished for. 



The two parents differed from one another in the shape of 

 the ears as well as in their behaviour with regard to the attacks 

 of yellow rust, the immune parent being dense-eared and the 

 susceptible lax-eared. In other respects they were very similar 

 to one another. Amongst the descendants of the original 

 hybrids there were three morphologically distinct types with 

 dense, lax, or intermediate ears. Both the power of resisting 

 disease and susceptibility to it were distributed uniformly over 

 these three groups. Thus dense-eared types similar to the 

 parent, but liable to the attacks of yellow rust, have been raised 

 together with immune forms similar in external appearance to 

 the susceptible Michigan bronze. 



The property of disease resistance, being recessive, will 

 breed true in succeeding generations. This has not been tested 

 in the case of the experiment described, but there is abundant 

 evidence for it obtained from other crosses. In one of these 

 cases four separate generations from the hybrids have been 

 cultivated, some of the forms in field plots in the open, and they 

 still show the same degrees of susceptibility to disease as the 

 two parents. 



Experimental evidence has also been obtained which indicates 

 that the immunity to other diseases to which cereals are liable 

 can be transferred in this same manner, so that it is not an 

 extravagant hope that one of the functions of the breeder will 

 be to mitigate the effects of these scourges by providing them 

 with unsuitable hosts. 



Up to the present most of the crosses have given unusually 

 simple results, and few of those complications due to the 

 presence of invisible factors such as have been investigated in 

 sweet peas and stocks, and in some cases in the animal world 

 have been met with, though it is by no means improbable that a 

 number exist. One interesting example of a compound character 

 has been seen, namely, grey colouring in the chaff, together with 

 the presence of hairs. The colouring is due to the presence of 

 pigment in the glumes. It is not due to the hairs themselves, 

 for many varieties of wheat have a rough or felted chaff and 

 no such colouring. On segregation the felting and the hairy 

 character always go together, all the rough chaffed forms being 

 grey and the grey chaffed rough. All attempts to separate 



