J. ARTHUR HARRIS AND H. S. REED. 



on the nature of the data on which the statistical methods are 

 illustrated are in order. 



By growth stage we mean any given moment of time at which 

 a series of organisms are measured. It is, therefore, synonymous 

 with age during the growth period. The absolute size of the 

 organism or of one or more of its parts a.t a given growth stage 

 is the only character of the organism available for consideration. 



By growth period we understand the period of time elapsing 

 between the sth and the j + ;/th growth stage. 



The increase in size during any such period we shall designate 

 as a growth increment. 



By relative growth increment, /,-, we understand the ratio of 

 the growth increment, r, to the absolute size of the individual at 

 stage, r, where r and s are any two successive stages. 



Turning now to the question of the original data as given in 

 Table I. of Reed s (1919) publication we note from a study of the 

 physical constants for absolute size in Tables I. and II. that there 

 is an increase in the mean height of the plants up to the //th day. 



TABLE I. 



STATISTICAL CONSTANTS FOR SIZE AT VARIOUS GROWTH STAGES. 



The increase from the 63d to the 7oth and from the /oth to the 

 77th day is relatively slight, being only 4.43 cm. or 1.79 per cent, 

 of the height for the 63d day in the first case and only 2.03 cm. 

 or 0.81 per cent, of the value for the 7Oth day in the second case. 

 The difference between the 84th day and the 77th day is negli 

 gible. In view of the fact that there is no appreciable growth in 



