Growth and variation in maize. 



157 



The question of most importance in this connection is in ree:ard 

 to the variation of the quintile distrilnitions of plants with different 

 mean quintile positions. For example, will plants which are relatively 

 small for the entire season be more or less variable than medium sized 

 plants? 



In tables 13 to 15 there is ^iven the average standard deviation 

 of the plants whose mean quintile position falls in the same class. Thus 

 from table 13 it is seen that the plants whose mean quintile position is 

 between 1-0 and I'S have an average mean quintile standard deviation 

 of 0-6658. The values of these mean standard deviations for the different 

 series are brought together in table 18. It wiU be noted that these are 

 the average standard deviations for these plants, obtained b}- averaging 

 the standard de'\iations of the plants in a class. This average stan- 

 dard deviation is entirely different from the standard deviation of the 

 combined frequency distributions of the plants in a class. This latter 

 standard deviation will be referred to later. 



Table 18. 



Average Mean Quintile Standard Deviations of Plants Havinj 



Different Mean Quintile Positions. 



From this table it is seen at once that the average standard devi- 

 ation of the end classes, that is of the very small and the very large 

 plants, are much smaller than the standard deviations of the plants in 

 the three middle classes. Also the standard deviation of the plants in 

 the middle class is larger than that of any other class. There is thus 

 an apparent difference in the variability of the large and small plants 

 on the one hand and the medium sized plants on the other. 



However, before drawing definite conclusions regarding these 

 variabihties, it must be remembered that plants with small or large 

 means cannot have as large standard deviations as the medium sized 

 plants. A plant which has a mean of 1-8 cannot have its observations 

 so widely scattered as a plant with a mean of 3-0. This can best be 



