76 



A MONTANE RAIN-FOEEST. 



of Asplenium and Diplazium with reference to each other is reversed, 

 but the remaining species sustain about the same relation to each other 

 and to the two ferns as in the preceding series. 



In table 22 are given the average hourly amounts of transpiration 

 for the five species, for each experiment with Set A and Set B. The 

 nocturnal readings of Set B shown in figure 6 are separated from those 

 of the following day in this table. 



When the averaged readings of transpiration for the five species, 

 during a series of periods in which all was subjected to the same 

 evaporation conditions, are compared on the basis of the rate of the 

 lowest one as unity, the following figures are secured, which may be 

 designated the coefficients of transpiring power: 



Table 28. 



A close relation is here brought out between the character of the 

 habitats occupied by these species and their coefficients of transpiring 

 power. Peperomia basellcefoUa is a plant of the xerophilous ridges, or 

 a mid-height epiphyte, while Peperomia turjosa and Pilea nigrescens 

 are found in the Slope and open Ravine forests, and Diplazium and 

 Asplenium only in the most hygrophilous of the Windward Ravines 

 (see coefficients for moist chamber, p. 104). 



RELATIVE TRANSPIRATION. 



The securing of the rate of evaporation concurrently with all transpi- 

 ration readings has made possible the determination of the rate of 

 relative transpiration — the ratio of transpiration to evaporation. The 

 ratios are determined by dividing the transpiration, in terms of the 

 loss per hour per square centimeter of leaf surface, into the evaporation 

 per square centimeter per hour from a free water surface. The trans- 

 mutation of the atmometric readings of evaporation into terms of free 

 water surface has been described on page 46. The relative transpira- 

 tion figures are a true index of the transpiration rate as determined by 

 the internal or physiological conditions of the plant and by the influence 

 of fight, in so far as its effects on the plant and the atmometer are 

 different. The fact that all work here reported was done in the shade — 

 in conformity with the conditions of the rain-forest — ^makes the error 

 of relative transpiration figures due to light effects less than it would 

 be in the case of experiments performed partly in the shade and partly 



