122 ILLINOIS ACADEMY OF SCIENCE. 



Hum, Primus virginiana, Vaccinium pennsylvanicum, Quercus alba 

 (seedlings), Ceanothus americanus, Asclepias tuber osa and other 

 characteristic shrubs and herbs. Three stations were placed here 

 about 50 meters apart, No. 6 on a fixed dune 12 meters high, 

 No. 7 on a slope 5 meters above the general level and No. 8 on 

 the floor of the forest. All were about equally exposed and 

 shaded. The resulting graphs show differences corresponding 

 closely to the elevation of their respective stations. The com- 

 paratively great elevation of the curve during the months of May 

 and October when the oaks were not in full foliage is worthy 

 of notice. The maximum for the summer months is 16 cc. per 

 day and the average for the three stations for the 178 days is 

 10.3 cc. per day. 



At Millers the vegetation exhibits no successional stages beyond 

 the oak dune, but 15 miles farther east, near the village of Otis, 

 Ind., there is a comparatively undisturbed tract of the cHmax 

 deciduous forest here dominated by the beech, Fagus grandifolia. 

 In parts of the forest sugar maple is fairly abundant, with occa- 

 sional trees of Tilia americana, Ostrya virginiana and Prunus 

 serotina. The undergrowth is principally seedlings of the trees 

 mentioned. Viburnum pubescens, Asimina triloba, together with 

 the usual mesophytic herbs. Here three stations were established, 

 but on account of the poor train service, readings were made 

 only every second week from May 30 to November 1. Station 11 

 was well surrounded by maple seedlings and largely shaded by 

 maple trees, station 12 was near a large beech tree on a slope 

 covered with a growth of Impatiens, and station 13 was in the 

 midst of beech seedlings "between two large beech trees. To- 

 gether they seemed to well represent the average conditions of the 

 beech forest. The resulting graphs were very similar and their 

 mean is used in comparison with those from the other associations. 



The maxima are in July and August, and amount to little more 

 than 12 cc. daily, the minimum occurs in September and is scarcely 

 3 cc. per day, while the average for the 155 days is 8.1 cc. per day. 



Several methods may be employed in comparing the data 

 obtained from the various evaporation stations. Perhaps the best 

 is to plot upon the same chart graphs representing the mean daily 

 evaporation by weeks from the several stations in the different 

 associations (Fig. 2). It will be seen that the graphs show several 

 similarities, but more differences. The maxima and minima are 

 generally coincident in time and proportionate in amount. All 



