1914] OTIS— TRANSPIRATION OF WATER PLANTS 471 



Results 



EVAPORATION FROM A FREE WATER SURFACE AND FROM A WATER 



SURFACE OCCUPIED BY EMERSED WATER PLANTS 



com 



summers 



number 



the evaporation from water surfaces. As would be expected from 

 a consideration of the various plants used, their differences of 

 growth, habit, and structure, together with the varying physical 

 factors, the results show considerable diversity in total and relative 

 amounts of evaporation. A vast amount of data has been recorded 

 throughout the course of the investigation, all of which it is 

 impossible to include in this paper. The statistical tables and 

 graphs which are published here for the most part summarize 

 the more detailed data. The results fall naturally into several 

 groups, which will be taken up successively. 



(a) Total amount of water evaporated 



Tables IV and V give in tabular form the amount of water 

 added to each tank, which represents the amount of water evapo- 

 rated by water and plant surfaces during any period, for successive 

 intervals. It will be noted that the total amount of water added 

 varies over a considerable range for the different tanks. If the 



amount 



from 



assigned, then the plants used in 1910 would stand in order of 

 evaporating power thus : pickerel-weed : cat- tail : arrow-head : great 

 bulrush : three-square rush : water lily as 1.98:1.88:1.55:1.19: 

 1.12:0.86. Using the plant combination indicated in table V, 

 the ratio would appear as follows: cat-tail : sweet flag: bur-reed: 

 pickerel-weed : great bulrush : water lily as 3.05:2.36:2.26:2.08: 

 1.20:0.89. The values for water lily (0.86 and 0.89) and for 

 great bulrush (1.19 and 1.20) are nearly the same for the two 



years. 



much 



due in part to the somewhat drier season and more exposed 

 situation and in part to a more luxuriant growth. The evapora- 

 tion from the water lilv tank was in both years much less than that 



