368 Spalding: Absorption of atmospheric moisture 



plainly manifest in the dried-up and discolored vegetation around.* 

 Various other species, notably Parkinsonia microphylla, Lycinm 

 Berland&ri, and some others, were also in full leaf, in striking 

 contrast with their condition the year before ; and this state of 

 things, coupled with the extraordinary relative humidity, which 

 for months had averaged approximately 60 per cent., as recorded 

 by the hygrograph, suggested as a possible explanation of the long 

 retention of their foliage the capacity of these plants to absorb 

 water vapor directly from the atmosphere, f The prompt reaction 

 of the ocotillo to increase of water supply, whether through root 

 or stem, had already been strikingly shown by the fact that this 

 species may form as many as five distinct leaf-coverings between 

 February and August, u the exciting cause in each instance being 

 an increase in the water supply" (through the root),* and also 

 that leaf-formation may be induced in four or five days by artificial 

 irrigation of the stem.§ It seemed worth while, therefore, to in- 

 stitute a special set of experiments in order to determine whether 

 this shrub, and some others with which it is associated, are capa- 

 ble of directly absorbing and utilizing the water vapor of the 

 atmosphere. 



The method employed is essentially the same as that adopted 

 in earlier experiments on leaf- absorption. Leaves and other aerial 

 parts were accurately weighed and then kept for varying periods 

 in a nearly saturated atmosphere, after which they were weighed 

 and differences of weight noted. 



The accumulation of more or less dew on one side of the re- 

 ceptacle employed in the experiments was taken to indicate a very 

 nearly saturated atmosphere where the plant was placed. No de- 

 position of dew on the surface of the plant was ever noticed, but 

 if in any instance this occurred, the conclusion drawn from the 

 results obtained is thereby strengthened. 



Beginning with the ocotillo, two lots of leaves were taken, the 



* While the aggregate rainfall for 1905 was 23.18 inches, that for the six months, 

 May to October, inclusive, was only 4.40 inches. 



f Cannon, W. A. The effects of high relative humidity on plants. Torreya 6: 

 21-25. 1906. 



X Cannon, W. A. On the transpiration of Fouquieria sphndens. Bull. Torrey 

 Club 32 : 397-414. 1905. 



§ Lloyd, F. E. The artificial induction of leaf-formation in the ocotillo. Tor- 

 reya 5 : 175-179. I9°5- 



