ELIMINATION 193 



With their results the student should make acquaintance through 

 their papers cited under Literature below. 



Another matter of new interest is a connection which has 

 been found to exist between transpiration and growth, a con- 

 nection so close as to make it possible, in certain cases, to use 

 the one as a measure of the other. The subject is discussed by 

 Livingston in the Botanical Gazette, 40, 1905, 178. 



The data the student has now accumulated will lead him 

 to an inquiry into the exact significance of transpiration to the 

 plant, whether it is a process of physiological value in itself, or 

 is merely incidental to other functions. For this he must make 

 himself acquainted with the present state of our knowledge of 

 the energy relations of transpiration, its possible connection with 

 the lifting oj the water threads in the ducts, and in how far it is 

 purely physical and how far physiological. And he should note 

 in what way the structures concerned in its performance are 

 related to those concerned in photosynthesis and respiration. 

 And he should give a clear exposition of this important subject. 



The copiousness of transpiration in conjunction with its 

 extreme sensitiveness to both atmospheric and soil conditions 

 makes the process the basis of very important ecological phenom- 

 ena; these the student should now work out and express, after 

 the same general plan which he has followed under photosyn- 

 thesis (page 113). 



Transpiration Quantities. These for forest and field plants are 

 summarized by Pfeffer, i , 250. For greenhouse plants, used in educational 

 work, they are given very fully in Miss Clapp's paper cited earlier under 

 Materials, a paper which also gives graphs expressive of the relations of their 

 transpiration to external conditions. She shows that the transpiration of 

 greenhouse plants in general has a mean of 48.73 grams per square meter 

 per hour during the day and 8.9 during the night, whence may 1 e derived a 

 conventional constant of under 50 gm 2 h for day and under 10 gm 2 h for night. 

 Her figures also demonstrate a range, taking day and night together, from 

 1. 12 through a mean of 28.81 to 257 grams per square meter per hour, which 

 may be expressed conventionally as 1-30-250 gn.Vi. 



Literature or Transpiration. In addition to the invaluable 

 works of Pfeffer and of Jost, there is a very important and satis- 

 factory monograph upon Transpiration, "Die Transpiration der 



