128 Ingvar Jorgensen and Walter Stiles. 
case shown in Fig. 2, but in which there is perfectly still air 
outside, so that shells are produced outside as well as in. Here the 
density of the gas will vary from p at a remote distance outside to 
p t at the perforation to zero at the absorbing surface. 
In the case of the leaf in still air, we are dealing with an 
approximation to this last case, but as in actual fact there will 
always be more or less movement of air outside the leaf there will 
be a corresponding approach to the conditions indicated in Fig. 2. 
If the partial pressure of carbon dioxide in ordinary air is called 
P, then in the last case, from Larmor’s formula, we have the quantity 
passing through any shell outside = 2k(P—P,)D, where D is the 
diameter of the perforation. Similarly, the quantity passing through 
any shell inside = 2kP,D. 
Now when a constant flow is established, these two quantities 
must be the same so that 
2k(P— P,)D = 2kP,D 
whence P—P, = P, 
or P = 2P y 
That is, in still air the pressure of carbon dioxide at the perforation 
will only be one half of the pressure of the gas there when this is 
kept constantly renewed. Consequently the diffusion gradients 
will only be half as steep in the former case and the rate of 
absorption will correspondingly be reduced to half. 
Similarly, in the case of the leaf, the rate of passage of carbon 
dioxide will be increased in the same way when the air outside the 
leaf is constantly renewed, provided that the cells surrounding the 
space into which the stomata open are perfect absorbers of the 
gas. Also, other things being equal, the velocity of flow through 
the stomata will be proportional, not to the areas of the stomata, but 
to their diameters. 
Since the surface of the leaf is perforated, not by one, but by 
many stomata, the researches of Brown and Escombe on diffusion 
through multiperforate septa become of great interest in relation 
to the intake of carbon dioxide. The multiperforate septa consisted 
of sheets of celluloid of thickness 0*08 to 0T mm. in which a series 
of holes at definite distances from one another were punched. The 
septa were fixed to the open ends of glass tubes containing sodium 
hydroxide. The following table gives some of Brown and Escombe’s 
results. In each case the area of cross sections of the tubes was 
measured and the diffusion through the perforate septum compared 
with that down an open tube. 
