SUMMARY. 



101 



the probable causes for failure of agreement with certain other 

 investigations have been indicated. The regulation of water-loss 

 was found to be controlled closely by the stomata when they are 

 nearly closed and by the factors of evaporation when they are wide 

 open. Brown and Escombe (1900) showed that diffusion of water- 

 vapor through the open stomata is much less than would occur if 



'MO 



110 

 lOt 

 90 

 80 

 70 

 60 

 50 



40 



I 



30 

 I 

 20 



1C 



z 



I 



\ 



10 II MT. I 



10 II NOON I 



FIG. 54. Series 33, showing transpiration from potted cow-beet plants 

 in dry soil (A) and from potometers (B). 



the air within the leaf were saturated. It therefore appears prob- 

 able that the air is saturated only in the deeper spaces of the leaf, 

 and that as the outer air is approached through the passages, sub- 

 stomatal chambers, and pores of the stomata, the saturation de- 

 creases to become more nearly like that of the air outside. As the 

 stomata close, the amount of saturated intercellular space probably 

 increases, and finally, when closure becomes complete, all the air con- 

 tained in the leaf becomes saturated. Therefore, water-loss is most 

 clearly affected by changes of stomatal opening when the openings are 

 approaching minimum. 



SUMMARY. 



1 . The stomatal movement of cut stems in 9 species of plants, in- 

 cluding Fouquiera splendens and Verbena ciliata, differs greatly from 

 that found in potted plants and field plants, except in the one exper- 

 iment with apple. Even in this case there was some divergence. 



2. Since the stomatal movement is different, the rate of water- 

 loss is also different from that of potted plants and presumably from 

 field plants. 



3. Lloyd's evidence that stomata are non-regulatory is therefore 

 vitiated by his use of potometers to measure the water-loss of field 

 plants. 



4. Although the factors concerned in evaporation have great 

 influence upon transpiration, this influence is definitely controlled 



