72 



A MONTANE RAIN-FOKEST. 



INDIVIDUAL VARIABILITY OF TRANSPIRATION RATE. 



Several experiments were performed which gave simultaneous 

 readings of the transpiration of two or three individuals of the same 

 species. In each case the individual plants used were from the same 

 spot in the rain-forest, were potted at the same time, and in every 

 respect treated in the same manner up to the time of experimentation. 

 The uniformity of soil-moisture conditions in the pots of the plants 

 which I used for experimentation has already been mentioned. In 

 spite of the apparent equivalency of the plants, and the fact that they 

 stood side by side during the experiments, the rates of transpiration, 

 when reduced to comparable areas, were found to differ to a considerable 

 extent. On August 6 three plants of Pilea nigrescens were run in par- 

 allel series and readings of their transpiration were taken simultane- 

 ously. The plants were designated A, B, and C (see table 23) and their 

 leaf areas were respectively 222 sq. cm., 326 sq. cm., and 360 sq. cm. 

 On adding the hourly quantities of transpiration per square centimeter 

 shown in table 23 the following totals are secured for the eight readings: 

 A, 4.70 mg.; B, 2.99 mg.; C, 2.12 mg. 



On September 18 two plants of Pilea, D and E, were run simultane- 

 ously (see table 23), and their areas were determined as: D, 427 sq. 

 cm. ; E, 205 sq. cm. The total of the hourly quantities of transpiration, 

 per unit area, for these plants is: D, 3.57; E, 4.74. 



On October 22, 23, and 24 three plants of Peperomia turfosa were 

 run simultaneously. Their leaf areas and collective transpiration 

 amounts per unit area are shown in table 26. 



On November 19 and 20 plants of Diplazium celtidifolium (see table 

 25) were run simultaneously, and the areas of leaf surface and the 

 total transpiration amounts per unit area were as follows: 



Table 27. 



Plant C. Plant D 



Area (in sq. cm.) 445 



Transpiration, November 19 11 .55 



Transpiration, November 20 7.07 



454 

 12.41 

 7.85 



Plant E. 



363 

 9.82 



