A STUDY OF THE RELATION OF TRANSPIRATION TO 
THE SIZE AND NUMBER OF STOMATA 
Walter L. C. Muenscher 
Considerable work has been done in determining the quantity of 
water lost from various plants under various conditions. Several 
extensive investigations have been conducted with a view of deter- 
mining stomatal values for various species. Although several im- 
portant researches have been conducted concerning the stomatal 
regulation of transpiration, very little has been done on the amount 
of transpiration in relation to the size and number of stomata per 
unit of transpiring surface. It was my aim to determine whether any 
relation exists between the amount of transpiration and the number 
of linear units of stomatal aperture per unit of leaf surface. 
I. Historical 
Probably the earliest attempt to determine quantitatively the 
amount of water lost in plants was by Hales (7) as early as 1727. 
Hales not only determined the amount of transpiration per square 
foot of leaf area for the sunflower, cabbage, grapevine, lemon tree, 
and apple tree, but he also found that the amount of transpiration 
varied during the day and night hours and also with changes in 
physical factors. 
Clapp (4) determined the quantity of water in grams transpired 
(GM^H) per square meter of leaf surface per hour for day and night 
for thirty common greenhouse plants both under greenhouse and 
under "standard" conditions, but she used only one individual of 
each species in her experiment. In com.puting the transpiring surface 
she considered only the upper surface of the leaf. She also found 
that there are two extremes of transpiration, the greatest amount in 
the early afternoon when the light is strongest and the minimum 
amount during the night when the stomata are closed. 
The work on transpiration up to 1904 is summarized in Burger- 
stein's excellent work on transpiration in plants (3). He discusses 
the various phases of transpiration, methods for its determination, 
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