98 A MONTANE RAIN-FOREST. 



with remarkable exactness from 6 a. m. until 2 p. m., after which hour 

 it continued to fall during the occurrence of a secondary maximum of 

 evaporation, culminating at 6 p. m. There is as much disagreement 

 as there is agreement in the curves of relative transpiration and stomata 

 movement from 6 a. m. to 4 p. m. The close parallelism of the trans- 

 piration and evaporation curves is very striking as compared with the 

 divergent behavior of the relative transpiration and stomatal curves 

 and points to the impotence of stomatal movements in counteracting 

 the influence of evaporation rate on transpiration, at least during the 

 mid-day hours. From 4 p. m. until 9 p. m. the curve of transpiration 

 lay below that of evaporation (plotted as one-tenth of the actual 

 readings), and during these hours there is a certain degree of correlation 

 between the relative transpiration and stomatal behavior: they fall 

 together from 4 to 6 p. m., but the rise in the relative rate between 6 

 and 9 p. m. is too great to be accounted for by the slight rise in stomata 

 openness. 



The series of stomatal readings ior Asplenium is unfortunately marred 

 by the loss of the 12 noon datum. Even in its absence, however, it 

 is possible to observe the fall of relative rate between 8 and 10 a. m., 

 accompanied by a constant stomatal openness, and the pronounced 

 fall of relative rate between 2 and 4 p. m., during an increase in stomatal 

 aperture. Here again, as in the case of Diplazium, there is a close 

 parallel between the rates of transpiration and evaporation until 4 p. m. 

 after which hour there is a parallelism between relative transpiration 

 and stomatal behavior that is entirely lacking through the earlier part 

 of the day. The opening up of the stomata between 6 and 9 p. m. in 

 Diplazium is still more pronounced in Asplenium, where the transpira- 

 tion rises with it. This occurs in both plants in spite of a sharply 

 falling rate of evaporation, and this also occurred at the same time in 

 Pilea nigrescens (fig. 17). 



If a correlation of relative transpiration and stomatal movement is 

 to be interpreted as proving that the latter controls the former, the 

 total evidence which I have secured indicates that stomatal move- 

 ments are of minor importance in regulation of transpiration. The 

 lack of a constant correlation between the relative transpiration behavior 

 and stomatal movement bears also on the question of the regulation 

 of stomatal openness by the water-content and other conditions of the 

 leaf, a problem on which I have no data. 



My experiments show, in general, that there is a lack of correlation 

 between the relative transpiration and stomatal movements during the 

 mid-day, and that in the late afternoon and early night there is a 

 positive correlation. This means that the evaporating power of the 

 air and the water-losing capacity of the plant stand in such a close 

 correlation during mid-day that the degree of stomatal aperture is 

 incapable of exerting a positive controlling influence. Under the lower 



