1914] OTIS— TRANSPIRATION OF WATER PLANTS 467 



same 



growing plants in the lake. Where 

 plants to work their way out of t 



common 



among the larger kinds, on account of their natural 



extreme 



them 



Scirp 



Sagittaria latifolia, Castalia odorata, Pontederia cordata, Typha 

 latifolia, Zizania aquatica, and Eichhornia speciosa. The two 



measurements 



com 



the Eichhornia floated awav the first time the raft sank. The 



remain 



for a period of two weeks, during which time they became well 

 established. 



At the beginning of the experiment measurements were made 

 of the area of leaf and stem surfaces exposed to the action of the 

 air. These measurements were made in the following manner. 

 In the case of those species having petioles and expanded blades 

 (as Sagittaria and Pontederia) , a tracing was made of every leaf blade 

 or portion of a leaf blade above the standard water level, and the 

 upper and lower diameters and length of the petioles above water 

 were recorded separately. Subsequently the area of blade surface 

 was ascertained by use of a planimeter and the area of petiole 

 surface was calculated as the area of the frustum of a cone. In 

 the case of Scirpus validus the height of the culm above the water 

 and its basal diameter were recorded, its surface being calculated 

 as the surface of a cone having the dimensions recorded. With 

 Scirpus americanus similar measurements were made, the surface 

 being treated as the surface of a pyramid whose base is an equi- 

 lateral triangle. The leaves of Typha were measured for the length 

 exposed to the air (not the height above the water) and the width 

 of the corresponding base, the surface exposed being calculated 

 by treating each leaf as a triangle whose base is the width and 

 whose altitude is the length given. Finally, a photograph of the 

 surface of the tank containing Castalia was made from a point 

 exactly above the center of the tank, since leaf tracings of the 



