EVAPORATION AND PLANT SUCCESSION: 
CONTRIBUTIONS FROM THE HULL BOTANICAL LABORATORY 147 
GrorcGe DAMON FULLER 
(WITH SIX FIGURES) 
The plant associations on the sand dunes of Lake Michigan 
have been described by Cowtes (1), who has called attention to 
the succession which is here so strongly marked and so easily deter- 
mined. In much of the region immediately south of the lake, the 
forest succession consists principally of associations dominated 
respectively by cottonwood, pine, black oak, white and red oak, and 
beech in the order named. These are usually designated the cot- 
tonwood, pine, and oak dunes, and the oak-hickory and beech- 
maple forests. They represent the major associations in a succes- 
sion extending from the pioneer trees to the climax mesophytic 
forest formation of the region. The dynamic physiography and 
the details of the composition of the various stages in the succession 
have been so thoroughly discussed by Cowtes that little further 
elucidation is necessary, but hitherto no attempt has been made to 
obtain any quantitative determination of any of the factors influ- 
encing this succession. 
The researches of LrvincsTon (2) and others have shown that the 
evaporating power of the air is a rather satisfactory summation of 
the atmospheric factors which determine the growth of plants 
during that portion of the season free from frost, and that it can 
be accurately measured by the porous-cup atmometer; accord- 
ingly, in the spring of rgro, a number of observation stations were 
established upon the sand dunes near Millers, Ind., and the rate of 
evaporation was determined during the ensuing growing season. 
Both the porous-cup atmometer devised by LrvincsTon (3) and the 
type described by TRANSEAU (4) were employed in this investi- 
gation. They were mounted in wide-mouthed bottles having a 
* A preliminary report of evaporation studies in the plant associations upon the 
sand dunes of Lake Michigan. 
193] [Botanical Gazette, vol. 52 
