Winifred E. Breinchley and Kharak Singh 201 



though the Hght intensity was apparently not affected. The environ- 

 mental conditions were as follows: 



Average weekly maximum temperature of house 23-6-31° C. 



„ ,, minimum „ ,, 10-0-15-3° C. 



Total hours of sunshine (per week) ... ... 21-52 



Daily average hours of sunshine ... ... ... 5-8 



In this case the crowded plants showed less difference among them- 

 selves than usual, the outer ones averaging 1-681 gm. against 1-339 gm. 

 for the inner. The spaced plants alongside were seriously harmed, and 

 only produced 1-055 gm. dry matter. 



The temperature records of the solutions were: 



In these spaced plants the mean maximum temperature was very 

 high, and for a period of seven successive days the solutions ran up to 

 above 29-7° C, the highest reading of the thermometer. The differences 

 between the day and night readings were therefore often large, although 

 the mean minimum did not fall below that of the outer crowded square. 

 A surprising difference w^as evident with the spaced plants on the side 

 bench. These grew well and strongly, looked better than any of the 

 crowded plants, and when cut averaged 2-171 gm. dry matter against 

 the 1-055 gm. of the spaced set under the more sloping roof, i.e. thev 

 were twice as heavy. Daily temperatare records were not taken for this 

 set, but on several occasions readings were made of all the solutions, and 

 they were always approximately the same for both sets of spaced plants. 



The relation of temperature to growth has been considered by various 

 workers, but generally in connection with the rate of growth of the roots 

 of seedlings during short periods covering a few hours at most. Under 

 these conditions Leitch(7) found that for peas 30° C. is a critical tempera- 

 ture above which growth is adversely affected, 28-30° C. being the 

 optimum, considered as the highest temperature at which no time 

 factor is operating. Lehenbauer(6), working with maize in water cul- 

 tures, showed that the optimum temperature varied with the period of 



