206 



BOTANICAL GAZETTE 



[SEPTEMBER 



as Monarda punctata , Asclepias tuber osa, and Opuntia RafinesqtiiL 

 This last station was maintained only during the seasons of 1910- 

 191 1 , and, owing to a series of accidents, its record was by no 

 means continuous, especially during the latter season. During 1910 

 (fig. 9) its rate of evaporation was decidedly in excess of that of 

 the other stations, especially in June and July. The records of 

 the other stations are quite comparable and their average appears 

 in fig. 4. 



1 



Fig. 8. — Dune covered with open forest of Quercus velutina; station 10; 



Miller, Ind. 



In 1910 (fig. 4) a maximum of nearly 19 cc. per day occurred 

 in May, before the trees were in full foliage, and similar high 

 rates at the same season of the year were seen in 191 1 (fig. 5)> 

 when it rose to the surprising height of 27.5 cc. per day; while in 

 1 91 2 (fig. 6) it was 21 . 5 cc. per day. This could hardly be a critical 

 period for vegetation, on account of the abundant supply of water in 

 the soil (see second part of this paper), although it might be decisive 

 for many young seedlings, and it may therefore be disregarded in 

 the general discussion. 



