Evaporation and Plant Habitats in Jam 



ing instrument. * The evaporating surface in both cases is a 

 porous clay cup, so connected by means of rubber stopper and 

 glass tube to a water bottle at a lower level that the cup is kept 

 constantly filled, the water evaporating from the moist clay 

 surface being replaced from the bottle. Readings are taken by 

 filling the bottle to a file mark on its narrow neck. Entrance of 

 rain water around the cork stopper into the reservoir, was 

 prevented by means of an apron of waterproof cloth. But this 

 arrangement does not prevent the backward flow of water 

 through the cup and tube during showers, so that the ordinary 

 form of instrument may be always expected to absorb rain water 

 to some extent. The non-rain-absorbing instrum.ent practically 

 obviates this difficulty by the insertion of a mercury valve 

 between the reservoir and cup, which allows free movement of 

 water from the former to the latter but not in the opposite 

 direction. The instruments stood side by side in their respective 

 stations and were so placed as to give the evaporation rate at a 

 height of from 15 cm. to 25 cm. above the ground. Filtered rain 

 water was used in the instruments, distilled water not being at 

 hand. 



The two stations were located on the grounds of the Cinchona 

 Laboratory of the New York Botanical Garden, in the Blue 

 Mountains. One of these was in an open, grassy clearing, in 

 the vicinity of the laboratory buildings, the other in a deep, 

 densely wooded ravine, about two miles from the first. At the 

 first station sunshine and wind had free access to the instru- 

 ments, at the second these were almost completely excluded by 

 the ravine walls and by the dense vegetation. Here the tempera- 

 ture was constantly much lower and the humidity higher than 

 at the station in the open, and the plants were usually covered 

 with a water film. While the soil in the open was covered with 

 grasses of ordinary types, that in the ravine bore a variety of 

 extreme tropical mesophytes. 



The instruments were read weekly for three weeks, from 

 May 22 to June 12, and records for a final period of four days 

 were also obtained. Likewise, approximate m,easurements of 

 the amount of precipitation at each of the two stations were 

 made. During the operation there was no period without rain, 



♦LiviuKSton, B. E. A rain-correcting atmocter for ecological iiiStrumentation. Plant 

 World. 13: 79 82. 1910. 



