1908.] 



Rust in Wheat. 



251 



"the proportion of immune to susceptible plants in such cases 

 heing again as one in three. 



In this generation then there were four fixed types of 

 wheat : — 



Immune " Club " wheat. 



Susceptible " Club " wheat. 



Immune lax-eared similar to Michigan Bronze. 



Susceptible lax-eared similar to Michigan Bronze. 

 Two of these resemble the parents, two show fresh com- 

 binations of the characters present in the parents. Further 

 trials are being conducted with these varieties in order to 

 demonstrate that these new character combinations are per- 

 fectly fixed. That they are so is predictable, and as a matter 

 of fact large trial plots containing tens of thousands of 

 individuals have been raised from somewhat similar crosses 

 in which no " reversions " to the parental forms could be 

 found. 



Those cultures from the susceptible wheats which produced 

 •a percentage of immune plants but were otherwise fixed proved 

 of some farther interest, for they provided a unique case of 

 plants of the same kind growing under the same conditions 

 but some attacked by rust and others rust free. The oppor- 

 tunity was therefore taken to obtain an estimate of the extent 

 of the damage caused by the disease. Numbers of each type 

 were harvested separately. The yield of grain of the diseased 

 plants compared with those in a healthy condition was in the 

 ratio of 0-2 to 1. The result, whilst undoubtedly far greater 

 than occurs in ordinary farming practice, will serve to show 

 how costly the cultivation of extremely susceptible varieties 

 may prove to the farmer. 



Determinations of the weight of the straw of diseased and 

 healthy crops were then made by weighing an equal number 

 of stems of the same length of each. The ratio of the weight 

 of the diseased straw to that of the disease free proved to be 

 as 1 in 2*5. The physical characters of the infected and 

 immune straw were strikingly dissimilar. In the case of the 

 former the surface was dull, the colour a dingy grey, and the 

 texture was soft and spongy. The straw of the immune types, 

 on the other hand, was a clean yellow colour, and the surface 

 was highly lustrous ; the separate steins were rigid and did 



