VARIATIONS OF THE WATER-BALANCE. 59 



The excessive rate of loss exhibited when the preparation was first 

 made continued with some diminution through the 155 days of the second 

 period of measurement, and not until after nearly 6 months of confinement 

 did the transpiration fall to a rate comparable with that of No. 1. 



On October 16, 1909, the weight was found to be 26.895 kg-., indicatiA^c 

 of a loss of 590 grams in 76 days, at the rate of nearly 8 grams daily. 



The singular action of this individual with regard to loss of water was 

 coupled with some remarkable variations in form or volume. On Novem- 

 ber 13, 1908, a space including two furrows and a rib was measured and 

 marked. On December 12 one furrow had narrowed and the other had 

 remained stationary. The whole circumference was measured and inter- 

 val marks established upon this circle. By May 12 a loss of 20 mm. was 

 shown on the circle, but this had not been steady in every portion of the 

 periphery. Each measurement included only a part of the line, from 

 which it is safe to infer that any given furrow or space between two ridges 

 might be contracted or widened by stresses set up in the plant from trans- 

 piration or other causes. Variations in diameter or circumference might 

 thus ensue which would be difficult of analysis unless a comprehensive 

 series of calibrations were made. The soft cylindrical trunk being not 

 homogeneous in its mechanical structure, the varying turgidity might be 

 expected to cause such irregular changes in form. 



On January 27, 1910, the weight was 26.795 kg., a loss of 100 grams in 

 103 days. Various tests applied during this long period indicated slight 

 gains in weight in some periods a few days in length, but the critical 

 amounts to be tested were below the coefficient of error of the scales used. 



On February 25, 1910, the weight was 26.725 kg.; loss, 70 grams in 31 days. 



On March 22, 1910, the weight was 26.625 kg.; loss, 100 grams in 25 

 days. The increase in the rate of transpiration was commensurate with 

 the heightened temperatures and lowered relative humidity. 



On April 21, 1910, the weight was 26.485 kg.; loss, 140 grams in 30 

 days, a rate of 4.6 grams daily. 



On May 13, 1910, the weight was 26.350 kg.; loss, 135 grams in 22 

 days, a rate of 6 grams daily. 



ECHINOCACTUS No. 7. 



On November 7, 1908, a large turgid plant was taken from the bajada 

 west of Tumamoc Hill and brought into the laboratory after the roots had 

 been neatly trimmed; 20 ripening fruits were included. The weight was 

 found to be 35.818 kg., and with mounting 37.595 kg. 



On December 8, 1908, the weight was found to be 37.040 kg., indica- 

 tive of a loss of 555 grams in 31 days, or a rate of nearly 18 grams daily, 

 which was something higher than No. 6, which was of the same origin 

 and received the same treatment. It is to be pointed out that the rate was 

 much higher than that of No. 1. 



