Cannon : Transpiration of Fouquieria 405 



A slight rain, not enough to induce the formation of leaves, 

 was recorded previous to the 12th. From subsequent experi- 

 ments on the influence of the rains on transpnation It was observed 

 that the rate may be increased without a change in the extent of 

 the transpiring surface, and it is possible that the small but posi- 

 tive change in the rate which was recorded in Experiment No. 2 

 is directly traceable to the earlier rain. 



In the experiments on the naked stems of Fouqideria it was 

 suspected that the hygrometric method did not reveal the true 

 condition of affairs inasmuch as it did not show how much of the 

 moisture which had been evolved from the plant was subsequently 

 absorbed by the dry branches. The affinity of air^dry stems of 

 Fouquieria for atmospheric moisture had been demonstrated in the 

 laboratory in the following manner : Leafless branches were 

 removed from the plant, the cut end was coated with vaseline and 

 the branch was placed in a beaker containing about two centi- 

 meters of water. The water very promptly ascended for several 

 centimeters the surface layers of the branch, which also increased 

 considerably in weight. The same behavior of leafless stems was 

 also observed outdoors. In every instance the portion of the 

 stem which had the affinity for water was the younger portion. 

 Later the outer cortical part of the branches is infiltrated with a 

 waxy substance which is impervious to water. To learn whether 

 air-dry stems would absorb water-vapor also the succeeding 

 experiment was devised. 



I 



Absorption of hygroscop. 



'The apparatus was set up in the same manner as if to determine 

 the transpiration but with the addition of an arrangement by which 

 air charged heavily with vapor was made to pass into the bell- 

 glass. As soon as the humidity of the air of the bell was increased 

 sufficiently, the openings into it w^ere tightly closed and the read- 

 ing of the polymeter was taken. The following is a brief of the 



experiment. 



Time. ^^^ ^^'^}- ^^ Temperature, 



saturation. 



Amount in 

 milligrams. 



10:25 65 83° F. ^76 



11:15 53.5 88 16S.7 



In 50 minutes the stems absorbed '] .1 milligrams of moisture. 



