468 BOTANICAL GAZETTE [December 



floating leaves could not be made without injuring them. By 

 means of the planimeter and a simple proportion the surface of 

 the leaves exposed was approximated. During the course of the 

 experiment, when leaves or parts of plants were for any reason 

 removed, the parts were measured and a record was made of the 

 date of removal. At the end of the experimental period all parts 

 above water were again measured and calculated in the same man- 

 ner as outlined above. In making calculations the slide rule was 

 resorted to wherever practicable. 



A second station was established in the summer of 191 1 in the 

 Huron River near Ann Arbor. The river at this place is about 

 60 m. wide. There is little or no natural protection on any side, 

 and it was necessary to inclose the entire station by a stationary 

 boom. The plants were in this case taken from the river near by. 

 They included Scirpus validus, Typha latifolia, Castalia odorata, 

 and Pontederia cordata used the first year, together with Sparganium 

 eurycarpum and Acorns Calamus. Owing to the withdrawal of the 

 water for a period of several weeks, while repairs were being made 

 on a near-by dam, the Sagittaria latifolia was all but destroyed and 

 could not be used. Consequently only eight tanks were used. 

 Two tanks were used as controls and the preliminary treatment 

 of the plants was the same as at the Portage Lake station. The 

 plants were not measured, however, and the surface area exposed 

 to the air was not ascertained. 



Just before measuring observations were begun, pontoons and 

 tanks were sunk to such a depth that the water in the tanks and the 

 water of the lake were in the same horizontal plane, which was 

 4.5! cm. below the level of the rim. 



Ecological and physiological aspects of plants used 



1. Scirpus validus Vahl. (great bulrush) inhabits the sti 

 at the margins of lakes, ponds, and quiet streams, or covers 

 shoals in lakes, often forming thick stands of large exten 

 maximum depth of water in which good growth occurs i 



The 



meter, while the denser stands are found in depths of 3-6 dm 

 tie culms are stout, terete, attaining a height of 2.5m. unde] 



