Growth and variation in maize. 117 



It is iateresting to note that the relation of tasseling to the 

 growth and variability of the height of corn plants it not unlike the 

 relation of puberty to the growth of children. This does not mean 

 that the two processes are necessarily analogous. 



Fi'oin the data presented it appears probable that the corn plant 

 grows in a series of cycles. Each cycle is characterized by the special 

 development of one set of organs. They are, in order, the root cycle, 

 the leaf cycle, the tassel cycle and the ear cycle. The reasons for the 

 postulatioii of these cycles is given in the text. 



Part II. 

 The Relation of Variation to Growth. 



In Part I of this paper we have discussed the general growth 

 curves and the question of variability for the height of corn plants at 

 the various growth stages. In the present portion we shall deal with 

 a phase of the growth problem which has hitherto received but little 

 attention. 



"^Hiat it is desired to ascertain is: how individual plants or groups 

 of plants having the same relative size at one stage are distributed in 

 the I'emaining growth stages? In other words, is there a definite ten- 

 dency for plants relatively small at one stage of their growth to be 

 relatively small in the other growth stages? Or again, is there a 

 tendency for certain individual plants to maintain a certain relative 

 size throughout the growth period, indicating perhaps a genotypic 

 difference in this respect? Or taking the other side of the question, is 

 there a tendency for plants relatively large at an early stage to grow 

 slower, and for plants relatively small at an early stage to grow faster, 

 so that in the end, plants of both kinds will, on the average, occupy 

 a mean position? What is the extent or degree of any of these ten- 

 dencies which may be found to exist? 



In the main such problems have been neglected by students both 

 of growth and of genetics. It seems, however, that some points of 

 interest may be gained by considering in detail the individual plants 

 which go to make up both the curve of growth and the frequency (or 

 variation) curve. Such methods have been of great value in the study 

 of genetics, and it seems probable that they may be of value in other 

 related physiological problems. The present paper attempts to make a 

 beginning in this direction. 



