1911] LIVINGSTON—LIGHT INTENSITY AND TRANSPIRATION 429 
measures of the relations which we wish to study in detail. But 
It is obvious that the first half-hour in any condition fails to give 
as clear an expression of the response to that condition as does 
the second half-hour, there usually being a more or less marked 
Fic, 1 
lag of effect behind cause; therefore we need give attention only 
to the second period in each condition. Thus a period of 30 minutes 
is allowed to elapse after each change of conditions before use is 
made of the data obtained. This is a common method for the 
