542 
Notes. 
a more perfect piece of mechanism than is required for the supply 
of carbon dioxide for the physiological needs of the plant, and 
instead of expressing surprise at the comparatively large amount 
of the gas which an assimilating leaf can take in from the air, we 
must in future rather wonder that the intake is not greater than it 
actually is. 
From data afforded by actual measurements of the various parts 
of the stomatal apparatus of the sunflower it is shown that an ex¬ 
tremely small difference of tension of the carbon dioxide within the 
leaf, as compared with that in the outer air, will produce a gradient 
sufficient to account for the observed intake during the most active 
assimilation. 
It is also shown that the large amounts of water-vapour which pass 
out of the leaf by transpiration are well within the limits of diffusion, 
and that it is unnecessary to assume anything like mass movement in 
the outcoming vapour. 
The translocation of solid material from cell to cell in the living 
plant is next considered, especially with reference to this transference, 
being, at any rate in part, brought about by means of the minute 
openings in the cell-walls through which the connecting threads of 
protoplasm pass. Notwithstanding the very small relative sectional 
area of these perforations they probably exercise an important function 
in cell-to-cell diffusion, in virtue of their properties as multiperforate 
septa. 
There are two appendices to the paper, one in which a full descrip¬ 
tion is given of a series of experiments on the absorption of carbon 
dioxide by solutions of caustic alkali from air in movement; the 
second being devoted to a detailed description of the methods used 
for accurately determining the carbon dioxide absorbed. 
