ECOLOGY. 343 



the plains station, increases most rapidly at the base station after the 

 second week. The transpiration per square decimeter varies inversely 

 with the altitude, as is also the case with wheat and oats. In both of 

 the latter the most rapid increase in leaf area was at the base station, 

 and this increase attained its maximum speed only after the second 

 week. In this all three species agree. 



The transpiration at the plains station varies roughly per unit of 

 leaf area inversely with the average temperature, evaporation, hu- 

 midity, and wind in the case of the sunflower, suggesting that light 

 is the paramount factor. With wheat the results are quite different, 

 the water-loss following changes in temperature, humidity, evapora- 

 tion, and wind. The response with oats is similar but somewhat 

 more complete. At the base station the unit transpiration follows 

 closely the temperature curve and roughly that of evaporation and 

 wind, but shows no relation to the humidity curve. At the subalpine 

 station there is no apparent correlation between the curve of unit 

 transpiration for the sunflower and the curves of average temperature, 

 humidity, and wind, and but a very remote correspondence with aver- 

 age evaporation. With wheat, but especially with oats, the transpi- 

 ration curve corresponds much more closely with those of temperature 

 and humidity. In dry weight the plains plants run highest, those at 

 the base station are slightly less, while the subalpine plants are but 20 

 to 30 per cent of those on the plains. The water requirement for sun- 

 flower is greatest on the plains, least at the base station, and inter- 

 mediate at the subalpine one. This is also true for wheat, but it is 

 least for oats at the subalpine station. However, in all cases, the differ- 

 ences at the various stations are small. If based on the green weight, 

 the water requirement decreases in all cases with the altitude, while the 

 succulence increases with the altitude. 



Behavior of Stomata, hy G. V. Loftfield. 



The present series of investigations into the behavior and efficiency 

 of stomata has been concluded during the year and the results sum- 

 marized. The studies of the year have dealt chiefly with the relation 

 between stomatal movement and transpiration, and partly with the 

 effect of physical factors upon the movement. A new phase of the 

 work has been an inquuy into the effect of stomatal movem.ent upon 

 respiration and gas-exchange. It was found impossible to correlate 

 the transpiration of a plant with its stomatal apertures unchanged with 

 the evaporation from several types of atmometers. This was found to 

 be due to the different natm-e of the response of plant and instrument 

 to various factors, especially light and heat. 



The experiments carried on at Tucson dealt primarily with Fou- 

 quiera splendens and Verbena ciliata, in the hope of explaining the dis- 

 crepancy in results of other investigators. A satisfactory explanation 



