Winifred E. Brenchley and Kharak Singh 209 



5. With very strong sunshine reduction of high maximum root 

 temperatures (from 29° C. upwards) allows of satisfactory growth, when 

 unprotected plants are rapidly killed. The inhibitory action of too high 

 temperatures at the roots is thus clearly shown. 



Nevertheless, the growth so made is less good than under more 

 normal conditions of insolation, thus demonstrating the harmful action 

 of too powerful sunlight, when all the root temperatures rule high. 



6. Eoot temperatures appear to be of greater importance than atmo- 

 spheric temperatures, as good growth can be made in hot atmospheres 

 provided the roots are kept relatively cool. 



7. There is some reason to beheve that the minima are of as much 

 importance as the maxima, i.e. that plants can withstand very high 

 maximum temperatures provided there is a considerable drop to the 

 minima, but cannot put up with the constant conditions of heat induced 

 by fairly high maxima and high minima. 



REFERENCES. 



(1) AsKENASY, E. (1890). Ueber einige Beziehungen zwischen Wachstum und 



Temperatur. Ber. d. Deuf. Bot. Gesells. vm. 61-94. 



(2) Balls, L. (1908). Temperature and Growth. Ann. Bot. xxn. 557-591. 



(3) Brenchley, W. E. (1919)-. Some factors in plant competition. Ann. App. Biol. 



VI. 142-170. 



(4) (1920). On the relations between growth and the environmental conditions 



of temperature and bright sunshine. Ann. App. Biol. vn. 211-244. 



(5) Keen, B. A. and Russell, E. J. (1921). The factors determining soil tempera- 



ture. Journ. Agric. Sci. xi. 211-239. 



(6) Lehenbauer, p. a. (1914). Growth of Maize seedlings in relation to temperature. 



Physiol. Res. i. 247-288. 



(7) Leitch, I. (1916). Some experiments on the influence of temperature on the 



rate of growth in Pisum sativum. Ann. Bot. xxx. 25^6. 



{Received June 10th, 1922.) 



Arm. Biol, ix 14 



