RELATION OF TRANSPIRATION TO STOMATA 
493 
any of these methods without modification. It was impossible to use 
the soHo paper method which was employed by Sampson and Allen 
(12), for it necessitated the making of many thousands of leaf prints. 
I made a number of preliminary determinations of the leaf areas of a 
number of plants by comparative weights, that is by weighing a given 
area of leaves which was determined by a Ganong's leaf-area cutter 
and then weighing the entire leaf area of a plant, from this proportion 
I determined the total leaf area of the plant. Then I also determined 
the leaf area of the same plants by making leaf traces and then com- 
puting the area by a planimeter. I found that the planimeter method 
was not only the most accurate but also the most practicable method 
for this problem. I found that the weight of one square centimeter of 
leaf varied from i to 100 percent from the average weight, depending 
upon the part of the leaf from which it was taken. The loss of water 
from the cut leaf sections is also very great especially if the leaves 
are not weighed immediately. By the weighing method the leaf 
area had to be found at the same time in all the plants of one species 
because the amount of photosynthate in the leaf at any given time 
varies with the time of day as well as from day to day. This would 
necessitate the determination of the weight per unit area each time it 
was desired to determine the leaf area for a number of plants. 
By the use of the planimeter one can find the leaf area of a plant 
regardless of the amount of water or photosynthate in the leaf and 
one can use the same method for almost any number or kind of plant 
at any time. But, because of the enormous number of leaves of 
which I had to find the area, it was found necessary to modify the 
method somewhat. I found that each species had a large number of 
leaves in each plant which were almost of the same size, so I sorted 
the leaves of each plant into five piles and measured the area of one 
leaf of each pile and then multiplied the area of one leaf by the total 
number of leaves in that particular pile and then I computed the 
total leaf surface for each plant in square centimeters, considering 
both the upper and lower surface of each leaf. 
Petiolar and stem areas were not considered as transpiring surfaces. 
It was found that these organs were practically free from stomata and 
the water loss from the same was very small in the plants used in this 
experiment. 
The leaf area was determined for each plant at the end of the 
experiment. Since most of the plants were small and had a small 
