86 Meriflelian Inheritance and Yelloir Jinst in WJimf 



On beds B and C the plants were also makinj; a very strong growth. 

 Owing to the large amount of space available, numerous tillers were 

 formed and the shoots were spreading out obliquely. 



On bed D the plants were about 18 inches high, erect, and of a light 

 green colour. They had tiliored much le.ss freely than the plants on the 

 other beds. 



Table XII shows that on this date all the plants of American Club 

 and of the two extracted resistant types (altogether '20F> plants) were 

 still entirely free from infection. Taking the proportion of plants infected 

 and the severity of attack into consideration, Burbank's was distinctly 

 the most susceptible type, 08 out of 72 plants being badly attacked. The 

 proportion of rusted plants in Wilhelmina and the two extracted sus- 

 ceptible types were very similar, hut the attack ou'Wilheimina was less 

 severe; the actual numbers were: in 7."j/7/f, .34 rusted out of 40 plants; 

 in 75/11 /(Z, 33 rusted out of 43 plants; and in Wilhelmina. 91 rusted out 

 of 121 plants. 



Confining our attention for the moment to the susceptible varieties, 

 we get some idea of the e.xtent to which "wide spacing,"' etc., apparently 

 favour rust attack. 



The effect of "wide spacing'" is seen by comparing beds C and D. 

 On bed D, out of 107 plants of the susceptible varieties, 73 were rusted, 

 i.e. 68 per cent. On bed 0, 21 out of a total of 23 susceptible plants were 

 rusted, i.e. 91 per cent. 



The effect of the heavy dose of nitrate is seen from a comparison of 

 beds A and D ; on the former, out of 1 24 plants of the susceptible varieties, 

 111 were rusted, i.e. 89-5 per cent, as compared with 68 per cent, on D. 



The combined effect of "spacing'' and "nitrate" is seen by-comparing 

 beds B and D. On the former, 21 out of 22 susceptible plants were rusted, 

 i.e. nearly 100 per cent, against the 68 per cent, on D. 



It is clear from these and other observations that very widely spaced 

 plants are more hable to an early infection than are closely planted 

 individuals — other conditions being equal. A partial explanation for 

 this possibly lies in the fact that widely spaced plants tiller more freely, 

 and so ofltcr a much greater area of leaf surface to infection than more 

 crowded individuals. On the other hand the percentage of early in- 

 fections on the closely planted bed A was as high as on the widely spaced 

 bed C, and it is unlikely that this effect was brought about by the in- 

 creased tillering of the plants on A. The increased susceptibihty of plants 

 receiving heavy doses of nitrogenous manures or extra space for growth 

 appears to depend rather upon the increased or modified food-supply 

 offered. 



