Notes * 
54i 
found to possess all the remarkable properties which had been 
anticipated. 
The material used for the septa was very thin celluloid, which was 
perforated at regular intervals with holes of about 0*38 mm. in diameter. 
Details of a number of experiments with such diaphragms are given, 
in which it is shown that they may be so arranged as to produce but 
little obstructive influence on the diffusive flow of a gas when the 
total area of the apertures amounts only to about 10 per cent, of 
the area of the septum, and that nearly 40 per cent, of the full 
diffusive flow may be maintained when the number of the apertures 
is so far reduced as to represent an area of only 1-25 per cent, of 
the full area of the septum. 
The explanation is to be found in the local intensification of the 
gradient of density in the immediate neighbourhood of the diaphragm, 
and which does not extend to the column away from the apertures. 
This disturbance of gradient is brought about by the rapid con¬ 
vergence of the lines of flux, and their divergence on the other side, 
with the consequent formation of a system of £ density shells ’ over 
each aperture. A system of perforations of this kind may be com¬ 
pared with a system of conductors electrified to a common potential, 
the density of the diffusing substance above the apertures corre¬ 
sponding to electric potential, and the non-absorbing portions of the 
diaphragm to a surface formed by lines of electric force. Just as 
the electric capacity of a plate is not much reduced by cutting most 
of it away, so also is it possible to block out a large portion of the 
cross-section of the diffusing column without materially altering the 
general static conditions on which the flow depends. 
The importance of these results in relation to diffusion through 
porous septa is next considered, diffusion through a thin porous 
septum being only an extreme case of free diffusion through a multi- 
perforate diaphragm, whose apertures are so far reduced in size 
as to materially interfere with the mass movement of the diffusing 
substance. 
A section of the paper is devoted to the application of these new 
observations to the processes of gaseous and liquid diffusion in living 
plants, and it is pointed out that the structure of a typical herbaceous 
leaf illustrates in a striking manner all the physical properties of 
a multiperforate septum. Regarded from this point of view it is 
shown that the stomatic openings and their adjuncts constitute even 
