68 
Knight. —On the Use of the 
intercellular spaces also increases. This has been the case in all the hypo- 
stomatous leaves investigated, and is in complete accord with expectation. 
As the stomata open, the resistance offered by them to the air-flow decreases, 
and that offered by the intercellular spaces remains approximately constant, 
so that, relative to the total resistance, that of the intercellular spaces 
increases as the stomata open. 
Another phase of the same phenomenon is evident in the differences 
in different plants. A plant whose stomata are large or are capable of 
wide opening, such as species of Eucharis, shows relatively a much greater 
intercellular space resistance than a plant with fewer or smaller stomata, 
as Enpatorium Raffilli. With the double chamber of dimensions stated 
above, 59 per cent, was the highest value obtained for the relative resistance 
of the spaces in Eucharis amazonica, whilst in Enpatorium Raffilli the 
value never rose above 18 per cent. 
The case of the amphistomatous leaf is somewhat different from that 
of the hypostomatous one. The double-chamber experiment with the 
former has not the same significance as with the latter, unless the stomata 
upon the surface opposite to that on which the chamber is fixed are 
blocked. 
Experiments of this type have been performed with the amphistomatous 
leaves mentioned in the above list, and all of them gave results comparable 
with those obtained with hypostomatous leaves. 
In an ordinary porometer experiment with an amphistomatous leaf, 
there is available for the air-stream a path directly through the leaf from 
one surface to the other, and it is probable that this direct path offers less 
resistance than the longer one which the air necessarily traverses in a hypo- 
stomatous leaf. It is therefore likely that the air will take the path 
of least resistance and pass directly through an amphistomatous leaf. 
A test of this can be carried out by a double-chamber experiment without 
previously blocking the stomata of one surface. If the resistance of the 
direct path is relatively small, then the greater part of the air will pass along 
it, and closing the outer chamber will have little or no effect upon the 
readings ; but if the resistance of the direct path is relatively large, some 
portion of the air-current will be diverted by closing the outer chamber, and 
a decrease in speed will result. 
In the case of Richardia, when neither surface was vaselined, the effect 
of closing the outer chamber was never more than 3 per cent.- — probably 
within the limits of experimental error — but when the stomata on one 
surface were blocked, the effect rose as high as 29 per cent. Dracaena, on 
the other hand, showed an effect up to 12 per cent., whether one surface was 
vaselined or not, the double chamber used having the same dimensions 
as that previously described. 
3. Owing to its simplicity of manipulation, the method just described 
