54 HORTICULTURAL SOCIETY OF NEW YORK. 



ance to plant life, viz., temperature, relative humidity, wind 

 velocity, and rainfall." 



Dr. Transeau and myself devised a plan for obtaining 

 evaporation data more definite than that at hand by asking the 

 assistance of numerous workers in the country to install and 

 operate the instruments for a widely distributed series of ob- 

 servations. The outcome of this plan was the cooperative ex- 

 periment mentioned in a previous paragraph. Data are at hand 

 for some thirty stations, but have not yet been sufficiently worked 

 over to warrant their being made public here; they will be pub- 

 lished at a later date. I am able to give at this time, however, 

 a good example of the differences in evaporation of stations at 

 different altitudes in the vicinity of Tucson, Arizona. Instru- 

 ments were installed on May I2th, I4th and i6th, in the Santa 

 Catalina Mountains at altitudes of approximately 6,000, 7,500, 

 and 8,000 feet. These instruments, were read on May 3ist and 

 June ist and gave the following average weekly rates: 6,000 ft., 

 238 cc.; 7,500 ft, 147 cc.; 8,000 ft, 133 cc. 



These instruments were placed at a height of 15 cm. above 

 the ground and were all in the open, but were surrounded at 

 some distance by the vegetation of the locality, the lower one by 

 scrub oaks, the middle one by open pine woods, and the upper 

 one by a denser growth of pine, Douglas spruce, etc. Later in 

 the season these instruments were injured by the action of im- 

 pure water, so that I am unable to give an average for a longer 

 period. These figures would suggest that the evaporating power 

 of the air plays a great part in the distribution of vegetation at 

 the different altitudes of a mountain range of this sort, a con- 

 clusion which would be expected from the work of Transeau 

 above mentioned. 



The President I am, myself, very glad indeed that this subject of 

 evaporation is receiving this attention, which is indicated by Dr. Livings- 

 ton's paper. I think we have not given a tenth of the attention we ought 

 to give to this subject of evaporation from plants. I have not the figures 

 at my fingers' ends about the amount of water evaporated by a tree in a 

 day. We have statements of the amount of water evaporated by a field 

 of grain, maze, in full vigorous growth. The amount of water evaporated 

 by an acre of any plant, say of clover, or anything of that kind, is given 

 to us, and it is staggering in the figures, and it certainly is a very im- 



