The Measurement of Variation 45 



that is, of the greatest frequency, is called the mode. 

 It is an excellent expression of type. When the group of 

 plants or population which is being studied is measured 

 and arranged with some suitable grouping, as illustrated 

 here, we see what the variety tends to do on the whole. 



Modal coefficient. It is desirable to know what per- 

 centage of the individuals falls into this group of highest 

 frequency, called the mode. This can be readily found by 

 dividing the number of individuals in this class (43) by 

 the total number (286) and multiplying by 100. This is 

 called the modal coefficient, and denotes the percentage of 

 individuals conforming to type. This modal coefficient is 

 .15 or 15%; that is, fifteen per cent of all of the plants 

 in this variety are found in one class. 



However, as this is dependent on the system of measure- 

 ment, one modal coefficient is not directly comparable 

 with another unless the same practice of measurement has 

 been used. Moreover, one could not compare the modal 

 coefficient of height directly with that of weight or any 

 other character of a different nature. 



It may readily be seen that a knowledge of the distribu- 

 tion of plants as represented by the mode or modal coeffi- 

 cient is of scientific and practical importance. It enables 

 the breeder at any time to spread out before himself a 

 fair representation of his variety. He can see at a glance 

 what is the prevailing type and in what direction and to 

 what degree his breeding is extending. 



Mean. There is another conception of type known 

 as the mean or average. One can understand that the 

 average height will differ in most cases from the 

 commonest height. The mean is most easily obtained by 



