TEMPERATURE. 



57 



mines in large measure the speed of the reactions occurring in the 

 leaf. ^\s soil-temperature, it affects the direct water-loss from the 

 soil and the growth and functioning of the roots. In all these cases 

 temperature plays an important though indirect part in the behavior 

 of the stomata. 



In one respect, however, temperature acts directly upon stomatal 

 movement, affecting the rate of morning opening. Such opening is 

 light-induced and hence dependent upon starch conversion, which is 

 undoubtedly an enzymatic process. It is to be expected that such 

 conversion will therefore follow the same law in regard to rate of 

 reaction as any other chemical reaction. No rigorous study of this 

 could be carried out, but inspection of the various series led to the 

 conclusion that possibly humidity changes and fluctuations of light 

 intensity within certain limits would not seriously affect the results 

 of the experiments attempted. These consisted in taking pots of 

 alfalfa kept in the dark-room over night into the sunlight on days 

 of different temperatures. It was realized that it was impossible 

 to allow for the effects of changes in light, humidity, wind, and other 

 factors, and hence the experiments were liable to serious error, but 

 on the whole the experiments agreed very well, and are at least 

 indicative of the general effect of temperature upon opening (fig. 30) . 



The plants were well-watered 

 the evening before and carried 

 into the dark-room. If condi- 

 tions were of the kind desired, 

 they were carried out and placed 

 in the sun the next day about 9 

 or 10 a. m. after stripping a leaf 

 for evidence that the stomata 

 were closed. Strips were then 

 removed at hour and half-hour 

 intervals on cold days and at 

 5-minute intervals on very hot 

 days, in order to determine the 

 time of maximum opening. There 

 was rarely more than 2F. dif- 

 ference between the temperature 

 of the dark-room and the air out- 

 side, and hence no error could be 

 expected from this source. As 



the light in each experiment was at least 80 per cent of the max- 

 imum for the region, light differences could hardly introduce any 

 serious error. Apparently, evaporation had little or no effect upon 

 this opening when it was not excessive, causing closure before or 

 shortly after maximum opening occurred. In all, 23 experiments 



HOURS 

 8.00 



7.00 



6.00 



5.00 



A-.OO 



3.00 



Z. 00 



1.00 



F 30 4-0 



c 6 



50 60 70 80 90 

 *0 20 30 



100 



FIG. 30. Relation of speed of total opening 

 to temperature. 



