TRANSPIRATION BEHAVIOR OF RAIN-FOREST PLANTS. 61 



brought into the laboratory for experimental use had been subjected 

 to the same frequent rainfall. The soil in which the plants were rooted 

 was, therefore, like that of the open, extremely moist, and the lowering 

 of moisture content to which it was subjected by the plants during 

 the course of any one experiment was too slight to be thought of as 

 affecting the transpiration rate. Most series were run for two days 

 without opening the sealed pots, but in several other cases the same 

 plants were opened at the top and bottom, set outdoors for a few days, 

 and then used again. 



For the short intervals of the transpiration experiments evaporation 

 was measured by weighing a porous cup atmometer, mounted in a 

 small glass jar (see plate 21 B). This method was more satisfactory 

 than the use of a burette, not only because of its greater accuracy, 

 but because it obviated the error due to the expansion and contraction 

 of the water column of the burette at morning and night. 



The area of leaf surface was determined by making blue prints of 

 the fresh leaves, cutting and weighing in the usual manner. The 

 figures given for area of leaf surface are twice the area of the blue prints, 

 except in the case of leaves coated at top or bottom. The total transpi- 

 ration of a leaf is therefore divided equally, in calculation, between the 

 upper and lower surfaces. 



All readings of transpiration in the following tables are given in terms 

 of the loss in milligrams per hour from a square centimeter of leaf 

 surface, and the evaporation amounts are reduced from the atmometric 

 readings to losses per hour in milligrams from a square centimeter of 

 free water surface. In plotting the diagrams the evaporation has been 

 divided through by 4 or by 10, as is indicated on each curve, it being 

 thereby possible to condense the diagrams. The readings given oppo- 

 site each hour are for the period closing at that hour, and the length 

 of the period is indicated by the hour given on the preceding line of the 

 table. The first hour given in each table is that at which the series was 

 set. In the diagrams the readings are plotted to the ends of the hours. 



The stomatal readings given in connection with several of the tran- 

 spiration series were made by the method used by Lloyd in his work 

 on Fouquieria. 1 The method was used in the manner recommended 

 by Lloyd, and the precautions mentioned by him were all taken, in 

 order to give this means of direct stomatal observation a thorough 

 test. Merck's absolute alcohol was used, and the supply bottle was 

 kept free of moisture by introducing a considerable quantity of dehy- 

 drated copper sulphate. Livingston and Estabrook 2 found that it is 

 unnecessary to use absolute alcohol in the operation of this method, 

 and that essentially identical results are secured with grades of alcohol 



, F. E. The Physiology of Stomata. Carnegie Inst. Wash. Pub. 82, 1908. 

 2 Livingston, B. E., and Estabrook, A. H. Observations on the degree of stomatal movement in 

 certain plants. Bull. Toir. Bot, Club .39 : 15-22. 1912. 



