104 



A MONTANE RAIN-FOREST. 



The rates of absolute transpiration obtained under moist-chamber 

 conditions are of importance in the general correlation of my experi- 

 mental work at Cinchona with my instrumentation within the rain- 

 forest proper. I have already alluded to the difference between the 

 hunaidity and cloud conditions on the windward and leeward slopes of 

 the Blue Mountains. My moist chamber experiments were performed 

 under conditions more nearly like those of the Windward Ravines and 

 Windward Slopes; the other laboratory experiments, however, were 

 carried on under the normal shade conditions of the Leeward Slopes, 

 on which the laboratory is situated. The low rates of absolute trans- 

 piration secured in the moist chamber may be taken as closely parallel- 

 ing the rates in the still air of Windward Ravines and in Windward 

 Slopes throughout the greater part of all normal days. In spite of the 

 approximate equality of the relative transpiration rates secured in the 

 moist chamber and those secured in the open laboratory, the fact remains 

 that the evaporation rate of the moist chamber and of the moist habi- 

 tats of the rain-forest is extremely low, and the equality of the relative 

 rates merely indicates that the transpiration is correspondingly low in 

 the latter situations. 



Table 44. — Coefficients of transpiration for open laboratory and for moist chamber. 



The plants of the Windward Ravines which were brought for experi- 

 mentation into the somewhat drier atmospheric conditions of the labora- 

 tory at Cinchona were subjected thereby to more active water loss. 

 The plants of the Windward Slopes and Ridges which were brought 

 into the laboratory were not subjected to so great a change from the 

 conditions prevailing in their natural habitats. By reason of this 

 circumstance it is instructive to compare the rates of transpiration of 

 the several species inter se under each of the two sets of experimental 

 conditions : the moist chamber and the open laboratory. It is possible 

 by such a comparison to determine whether the rates of transpiration 

 of the several species from different habitats stand in the same relation 

 to each other under the Leeward Slope conditions of the laboratory 

 at Cinchona and the Windward Ravine conditions of the moist chamber. 

 This is best done by totaling the amounts of absolute transpiration 

 for simultaneous periods and reducing the totals to the basis of the 

 lowest as unity. Such figures have already been given for the labora- 



