YIELD AS AFFECTED BY SUSCEPTIBILITY TO COLD. 



101 



per cent survived are grouped together. In the next class are all 

 plants of which from 20 to 30 per cent survived. The other classes 

 increase by 10 per cent surviving plants until 70 per cent is reached. 

 All plants of which more than 70 per cent survived form the last class. 



Table 30 gives a summary of Table 29, the averages for each class 

 being shown. From this table it will be seen that with an increase 

 in the proportion of surviving plants there is an increase in the 

 weight of grain per plant and in the number of kernels per plant. 

 It is therefore to be concluded that decrease in 3'ield from winter- 

 killing is due not only to the loss of plants that are destroyed, but 

 also to a decreased yield from most of the surviving plants. 



Table 30 also shows that the weight of the average kernel is not 

 affected by the freezing of a large proportion of the famil}-, the 

 decreased yield being due, it may be assumed, to the decreased 

 number of kernels, owing to a decreased ability to tiller. 



With an increase in the proportion of surviving plants there is, 

 perhaps, a slight decrease in the percentage of proteid nitrogen in 

 the kernels and in the number of grams of proteid nitrogen in the 

 average kernel, although this is so slight and so irregular that it 

 would not be safe to draw any conclusions from it. The total pro- 

 duction of proteid nitrogen per plant naturally increases. 



Table 29. — Yields of plants, arranged according to percentage killed in each family. 



10 TO 20 PER CENT. 



