24-1: Relations between Growth and Environment 



though the mean rate of growth is lower when food is scarce. During 

 the first period the excess of food has no significant effect upon the rate 

 of growth, but during the second period the mean differences in the 

 rate of increase in the presence of abundance and of scarcity of food 

 are strongly significant in favour of the well supplied plants. 



8. During the early weeks, corresponding approximately to the 

 first period of growth, the shoot/root ratio falls, owing to the steady 

 increase in root weight which is associated at first with a decrease and 

 later wdth an increase in shoot weight. During the second period of 

 active growth the shoot increases in weight far more rapidly than the 

 root, and thus the shoot/root ratio rises steadily. Increase in shoot 

 growth is closely associated with rise in temperature, though the lowest 

 mean maximum attained in the experiments did not cause a cessation 

 of growth. Root growth is much affected by low mean maximum tem- 

 peratures and practically ceased, under the experimental conditions, 

 when they were consistently below 60° F. Rise in maximum temperature 

 had much less beneficial action upon the roots than upon the shoots. 



9. In early stages of growth the amount of nitrate absorbed by the 

 plant is relatively large in comparison with the dry matter produced, but 

 later on more dry matter is formed in proportion to the same amount 

 of nitrate, owing to the accumulation of the products of assimilation. 



In conclusion I wish to express my indebtedness to Mr R. A. Fisher, 

 who has examined the figures and has furnished me with the statistical 

 information embodied in this paper. 



NOTE. 



SOME FACTORS IN PLANT COMPETITION 



(THIS JOURNAL, VOL. VI, NOS. 2 AND 3, 1919.) 



By an oversight the weights of the barley and mustard seeds, used in the calculation 

 of the efficiency indices, were omitted. 



Mustard. Tables I— II, pp. 14.5—147. Average wt. per seed -007 gm. 

 Barley. Tables III— VI, pp. 149— 150. ,, ,, 055 ,, 



Barley. Tables IX— XVI, pp. 162—167. ,, „ -065 ,, 



In each case the efficiency indices are per cent, per day. 



