Growtli ami variation in maize. 105 



Changes in the Mean Height. 



The means of the several series as efiveii in fnliles 1 to 6 are 

 shown graphically in fig. 1. 



From this figure it is noted that the plotted means give in each 

 case a relatively smooth growth curve. It has been shown by a number 

 of authors, particularly in the excellent papers by Donaldson and Hatai, 

 that the growth of an organism can usually, if not always, be described 

 by a logarithmic curve of the general type, 

 Y = a -|- b log X. 

 There is no longer any question as to the value of such curves in 

 describing growth data. Recently Hatai ('11) has been able to give a 

 more definite physiological interpretation of the logarithmic curves. The 

 present gi'owth data have not been fitted with theoretical curves chiefly 

 because we desired to devote our efforts to other growth problems. 

 Further the character here measured (height of plant) does not take 

 account of the whole of the growth of the corn plant. This fact 

 introduces certain peculiarities into the data. 



If we could have taken the weight of the entire plant at each 

 date, the growth curves would undoubtedly have been quite different. 

 As will be pointed out later, there is considerable evidence of cyclical 

 periods of growth in the corn plant. Thus for some time after the corn 

 comes through the ground it is probable that most of the growth occurs 

 in the root system. This growth is not shown in our measurements. 

 Again, as will be pointed out below, as soon as the tassel blooms the 

 plant absolutely ceases to grow in height, although the ear continues 

 to grow very rapidly. Thus our data show the growth to cease veiy 

 suddenly about August 1, while as a matter of fact the plant continues 

 to gain in weight for a long time after this. However, these facts in 

 no way invalidate the present data for the purpose for which they were 

 collected (cf. Part II). 



Considering first the leaf measurements (Series A, B and C) the 

 curves as they stand may be divided into two princii)al phases. The 

 first phase extends from the beginning of the measurements to July 3 

 and the second from July 3 to July 27 at which time the plants have 

 completed their growth, so far as leaf measurements are concerned. 

 The first of these phases could be fitted reasonably well by a straight 

 line although if we had measurements from the time the plants came 

 through the ground we should probably find the curve tailing off 



