74 Knight . — On the Use of the 
tendency for changes in one curve to be accompanied by similar changes in 
the others. 
A. B. c. 
Area ... i-o sq. cm. i*o sq. cm. i*o sq. cm. 
Mean reading 0*128 0*317 0*193 
It is clear that the stomata of the mature healthy leaf were more 
widely open than those of the very young or very old leaves, whilst from the 
curves it may be seen that the stomata of the mature leaf were capable of 
closing to an aperture as small as those of the other two. 
Similar results were obtained with Ficus elastica and Etipatorium 
Rafjilli. 
Fig. 7* Behaviour of stomata on different leaves under similar conditions. Eucharis Mastersi. 
The generalizations as to the relative size of stomatal pores on different 
parts of a plant are made on the assumption that the stomata are evenly 
distributed over all leaves. To test this, several countings were made 
of the number of stomata per unit area of epidermis on leaves of Eucharis 
Mastersi and Ficus elastica. 
From the results it appears that the region nearest the edges of the leaf, 
particularly near the apex, is more thickly covered with stomata than the 
more central portions, in some cases the ratio being as large as 1*4 : i*o ; but 
at quite a short distance from the edge the numbers are almost the same as 
those near the midrib. 
In the case of leaves of different ages there is a distinct gradation — the 
old leaves having most and young leaves fewest stomata per unit area, 
the largest ratio observed being 1*3 : i*o. 
Thus in the porometer experiments upon one leaf only, the chambers 
were never near enough to the margin to be affected by the irregular 
