TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 73 



The figures given for the three species indicate that all of them 

 show variability in the amounts of their transpiration, sometimes slight, 

 sometimes considerable. The fact that the plants in each series were 

 placed side by side during the determination of their transpiration 

 amounts, and were therefore under identical atmospheric conditions, 

 together with the fact that the soil character and soil moisture were 

 so nearly identical as to be incapable of exerting an influence on the 

 available water supply, points to internal, physiological factors as 

 causing the differences. There is evidence in the cases of Pilea and 

 Diplazium that the plants which have smaller leaf area have higher 

 transpiration totals, indicating a greater transpiration activity on 

 the part of the smaller and younger plants. For Peperomia, however, 

 these relations are reversed, at least on the second and third days, two 

 plants of different area having almost identical totals on the first day. 



Such differences of behavior between plants of the same species under 

 such nearly identical conditions is probably true of very many functions 

 other than the transpiration. A row of plants grown in greenhouse 

 or garden from the same seed, planted at the same time, with identical 

 water supply and soil, will grow at different rates. Differences in 

 growth rate and other activities may often be observed in plants grow- 

 ing in their natural environment, although in the field it is always more 

 difficult to be assured that the environmental conditions are so nearly 

 equal as under glass or in the garden. Such differences of individual 

 activity are an index of differences in the character or intensity of the 

 many functions being performed by the plant, and may well be corre- 

 lated with such differences in individual functions as have been shown 

 to be true transpiration. There is apparently no definite specific 

 rate of transpiration for the rain-forest plants investigated, although 

 each species fluctuates around a normal rate for a given set of conditions 

 and the limits of variability are different for different species. 



CONCURRENT RATES OF TRANSPIRATION IN DIFFERENT SPECIES. 

 Several experiments were performed in which five plants of different 

 species were run concurrently, with a view to ascertaining the degree 

 of similarity or difference in their transpiration behavior under the 

 same atmospheric conditions and to comparing the amounts of water 

 loss from the different species; also, in view of the individual varia- 

 bility of transpiration, to discover any possible changes in the relation 

 of the species to each other as respects transpiration amount, in dif- 

 ferent series of the same sort. The species used for these experiments 

 were Pilea nigrescens, Peperomia turfosa, Peperomia basellcefolia, Dipla- 

 zium celtidifolium, and Asplenium alatum, the habitat differences of 

 which have already been mentioned. Two sets of the five species 

 were used. The entire series of readings for Set A is shown in table 19, 

 those for Set B in table 20 (see figs. 5 and 6). 



