6(3 JOURNAL OF FORESTRY 



power of the air. A rather close agreement was found in the evaporat- 

 ing power of the air in the various communities ; the prairie was always 

 the most xerophytic. 



The following conclusions are quoted from the lirst monograph : 



"The great amount of evaporation in the prairie coupled with low 

 water content of the soil is a sufficient cause for the xerophytic char- 

 acter of the vegetation. It shows also the difficulties met by trees in 

 establishing themselves in grassland and may explain their absence 

 from the prairies. 



"Plants placed in the more mesophytic scrub community transpire 

 much less vigorously than others of the same species placed in the 

 prairie. In general, there is a correlation between the evaporating 

 power of the air and the amount of transpiration. 



"If sufficient light is available, there is no question but that humidity 

 of the air and the soil are the most important factors attecting the 

 establishment of the different plant communities. The progressive 

 increase of the humidity of the habitat causes a corresponding increase 

 in the mesophytism of the plant community. This change of plant 

 population from the xerophytic to the mesophytic type is a phenomenon 

 called succession. 



"The evaporation rates and the amount of soil moisture in the various 

 communities both in Minnesota and Nebraska vary in general directly 

 with the order of their occurrence in the succession, the community 

 nearest the climax being the most mesophytic in both respects." 



Pool, Weaver, and Jean in a second monograph present the results 

 of a continuation and considerable extension of these studies in 1917 

 at the stations in the prairie and woodland near Liticoln, and also 

 much additional material from a new series of stations near Peru, on 

 the Missouri River. This latter paper also presents many experi- 

 mental data bearing on the successional sequence of the various wood- 

 land types as are commonly developed about Peru. In addition to the 

 analysis of the physical factors, the authors have added quantitative 

 analyses of the vegetation. Charts of belt transects similar to strip 

 surveys of the forester, showing the exact number, diameter, and 

 position of every woody plant growing on the area are strikingly 

 illuminative. In fact, many of the quantitative data are ^hown graph- 

 ically in a very convincing style. 



The author's conclusions are quoted from the second monograph 

 as follows : 



"This paper contributes data which still further substantiate the 

 conclusions drawn from previous investigations that evaporation rates 

 and soil moisture conditions in the various plant communities studied 



