STOMATA. 137 



rapid change much more marked quantitlve responses may 

 be induceti. If a plant is removed from total darkness and 

 placed in bright illumination, there follows a marked in- 

 crease in the rate of transpiration. The inverse change is 

 followed by an inverse response. Is this increase or decrease 

 due to a correlated change in the size of the stomatal open- 

 ings? If so we should Hnd that the maximum transpiration 

 rate is reached simultaneously with the maximum stomatal 

 opening. The fact appears, however, to be far different. 

 Without giving tedious figures, it may be said briefly that 

 with little or no movement in the stomata, and therefore 

 with little change in the size of their openings, wide fluctua- 

 tions in the rate of transpiration may and do occur, and so 

 far as experience shows, the maximum possible rate of trans- 

 piration, judging from the size and number of the stomata, 

 has not been observed. Brown and Escombe found, for ex- 

 ample, in the sunflower, that the observed maximum rate of 

 transpiration was only one-sixth the possible rate supposing 

 the full diffusive capacity of the stomata to occur. It appears 

 further to be true that the loss of water from the plant 

 through the stomata may be so great that wilting may ensue 

 and progress for a not inconsiderable period, before the 

 stomata begin to close. Thus the eftectiveness of these or- 

 gans as regulators of water loss is so slight that even when 

 the danger is great, it is met only in a very tardy and insuf- 

 ficient way. This is further shown to be the case by the ob- 

 servation that the removal of a plant from a damp atmos- 

 phere to a dry one does not lead to the closure of the stomata 

 unless the change is one sufiicient to cause wilting, when the 

 stomata close the movement of closing being caused by the 

 loss of water from the leaf as a whole, and not as a check 

 becoming effective before wilting sets in, a view held by Fran- 

 cis Darwin, 



By way of summarizing, then, we may conclude that, 

 for the present, and in the light of the facts obtained by 

 the methods used, the evidence now in hand does not support 



