156 



EARL E. SHERFF 



stolonifera, C. Amomum, Cephalanthus occidentalis and Salix lon- 

 gifolia, and passes in turn thickets composed of Samhucus cana- 

 densis, Populus tremuloides, and taller species of Salix, forest com- 

 posed largely of Quercus bicolor, Q. rubra, Fraxinus nigra, F. 

 americana and Ulmus americana, and finally reaches a forest 

 composed of Quercus rubra and such upland species as Q. alba, 

 Q. coccinea and Carya ovata. 



Li\dngston, in his well-known studies of transpiration, found 

 that, in a general way, the measure of transpiration in plants 

 was fairly indicative of their respective environmental conditions. 

 The transpiration rate for most plants being roughly propor- 

 tional to the rate of evaporation of water from a partially open 

 receptacle, he introduced the porous-cup atmometer for measur- 

 ing the evaporation rate of water. Four of these atmometers' 

 were set out May 21, 1911, at different stations indicatd on the 

 map ; — an instrument at station 1 , near the edge of Skokie Stream ; 

 one at station 2, in the outer part of the reed swamp; one at station 

 3, in the outer part of the swamp meadow, and one at station 4, 

 in a stretch of forest east of the marsh. Instrument no. 1, was 

 in the center of a dense growth of Typha latifolia. As the sum- 

 mer advanced, plants of Scutellaria galericulata and Teucrium 

 occidentale grew up in the shelter of Typha. No. 2 was surrounded 

 by Iris versicolor, Sium cicutaefolium and a few plants of Typha. 

 No. 3 was in a dense growth of Calamagrostis canadensis, and 

 no. 4 in a small area of pastured forest, composed chiefly of Quer- 

 cus bicolor and Fraxinus americana, also a moderate proportion 

 of F. nigra. The unglazed part of each porous cup extended 

 from about 22 cm. to about 28 cm. above the ground, gi\'ing a 

 mean height of 25 cm. Readings were taken weekly, up to and 

 including October 15, 1911. After correction according to the 

 method outlined by livingston,* they were plotted graphically, 

 appearing as shown in figure 2. The ordinates represent the 



' None of the atmometers used were provided with a rain-excluding device, 

 such as recommended by Livingston (Livingston, B. E., Plant World 13: 79-82. 

 1910). 



Livingston, B. E., Evaporation and plant development. Plant World 10: 

 269-276. 1907. All four atmometers were restandardized in the middle of August 

 and at the close of the work. 



