84 A MONTANE RAIN-FOREST. 



mum rates of Livingston for Tribulus, Allionia, and Boerhaavia. Also, 

 my own relative rates for herbaceous species of the rain-forest flora, 

 investigated in the shade, exhibit a lower range of maxima than do 

 the plants used by Livingston. If, however, these rain-forest plants 

 had been placed in the sun their relative rates would have mounted to 

 much higher figures, because of their thin epidermis and light cutiniza- 

 tion, taken together with the fact that the high humidity is deterrent 

 to rapid evaporation even in the sun. A test made by placing a plant 

 of Pilea nigrescens in full sunshine from 9 h 30 m to 10 h 30 m a. m. gave a 

 relative transpiration rate of 0.238, which is twice as great as the highest 

 shade rate secured for this species. The same plant was kept in the 

 sun from 10 h 30 m to ll h 30 m (there being a few minutes of cloudiness 

 in this hour), and the relative rate fell to 0.193, although the evapora- 

 tion fell only from 22 to 21 mg. Other tests made in the sunshine 

 with the more hygrophilous Asplenium and Diplazium showed them 

 incapable of withstanding direct insolation for so much as one hour, 

 and although the wilted condition of their leaves indicated a high water 

 loss they were not weighed at the ends of the periods. 



The fact that the relative rate of Pilea in the shade was doubled by 

 placing the plant in full sunshine gives at least some warrant for 

 estimating that the relative rates of the other herbaceous species would 

 be increased in the sunshine to double their shade values. If such 

 approximate values for the relative transpiration in the sunshine be 

 taken for the herbaceous plants of the rain-forest, they will be of the 

 same general order of magnitude as Livingston's rates for the desert 

 ephemerals, and both of these classes of plants will exceed, in general, 

 the rates secured by Mrs. Shreve for Parkinsonia. 



The minimum rates of relative transpiration are extremely variable 

 in any number of experiments with the same species, and their signifi- 

 cance in comparison is not so great as that of the maximum readings. 

 The highest minimum rates found among the data which are under 

 comparison are those of the hygrophilous ferns of the rain-forest, while 

 the lowest of the rates for Peperomia basellcefolia are of the same general 

 order of magnitude as those for the desert ephemerals and for Parkin- 

 sonia (see table 31). 



It is possible to say, in summarizing, that the most nearly xerophilous 

 of the rain-forest plants exhibit about the same maximum relative 

 transpiration rates as do the most nearly hygrophilous of the desert 

 herbaceous species. The relative rates for herbaceous plants of the 

 rain-forest, as determined in the shade, are about half of the rates for 

 the desert ephemerals, as determined in the sun, and there is some 

 evidence that this difference is due to the fact that one set of experi- 

 ments was performed in the sun and the other set in the shade. The 

 rates for Parkinsonia, determined in the sun, are of about the same 

 general order of magnitude as the shade rates for the Jamaican her- 

 baceous species. 



