82 Clyde E. Leighty 



large amount of such work. Biometrical methods are used in this 

 study, the various constants determined being the mean, the standard 

 deviation, the coefficient of variabihty, the coefficient of correlation, and 

 the probable error of each of these. 



It is important to know these values for any plant for whose improve- 

 ment breeding efforts are being made. Such statistical data should 

 largety direct the efforts and add definiteness to the operations. The 

 mean enables one to know what any strain or variety is likely to do, on 

 the average, in its various characters. The standard deviation and the 

 coefficient of variability are indices of variation: the former is perhaps 

 the best index of variation that is in use for the same or hke characters 

 of different lots of material measured in the same units; the latter is of 

 value when the variations of unlike characters of different lots of material 

 measured in dissimilar units are compared. 



Rietz and Smith (1910 : 296) ^ define the correlation coefficient as 

 follows: "The correlation coefficient may be defined as the mean product 

 of deviations of corresponding variates from their mean values in units 

 of the standard deviations." The correlation coefficient is of especial 

 value in relation to selection. In the processes involved in selection for 

 any one character, several other characters may at the same time be 

 modified mcidentalty. By the modification of such characters the cor- 

 relation in succeeding generations may be modified in inexplicable ways 

 unless the correlations of the parents are known. Again, the actual 

 work of selecting desirable plants is dependent on the correlations that 

 exist in the plants themselves. For example, if the purpose of selection 

 is to increase yield, the relation of this character to height is often of 

 importance. 



These studies are not exhaustive, nor could they well be made so. 

 Certain correlations have been determined for several varieties of oats. 

 No inheritance studies are here included. These results must therefore 

 be considered as being preliminarj- to such studies, for it is of fundamental 

 importance to know the correlations that exist between the different 

 characters of the parental plants before definite and intelligent progress 

 can be made in the study of inheritance, which is the correlation that 

 exists between parents and offspring. 



3 Dates in parenthesis refer to " Literature cited," page 215. 



