Equilibrium in the Intake of Dyes by Discs of Plant Tissue. 521 
internal concentration and the external concentration of the dye when equi- 
librium was reached. He found that in many cases the ratio was of the order 
x 1 1 
- = — , or — , 
y 120’ 240 
or even less, where x = the final internal concentration, and y — the final 
external concentration. 
3 . Influence of the size of the molecule. 
Th£ dyes which were employed in the present investigation may be 
classified with regard to the size of the molecule, as follows: — 
Colloid Semi-colloid Crystalloid 
Congo red Methyl violet Methylene blue 
Aniline blue Neutral red % Eosin 
It is evident, therefore, that in the case of crystalloids and semi-colloids, 
the size of the molecule has little influence in determining the amount of the 
dye absorbed ; this is in agreement with the earlier conclusions reached by 
Ruhland ( 5 ), though in his later work he completely altered his attitude. 
Neither of the dyes classed as colloids, however, was absorbed in any 
appreciable quantity ; the case of aniline blue is especially interesting, as 
this dye is basic, and was the only basic dye investigated which was not rapidly 
absorbed. It is noteworthy that Pfefifer recorded the fact that aniline blue 
is not absorbed by plant tissue. 
4 . Comparison of the results obtained with living and dead, tissue. 
If the results recorded in Table II are compared with those in Table V, 
it will be seen that the discs of dead tissue behaved in a very similar manner 
to the discs of living tissue. In every experiment the absorption was slightly 
less in the case of dead tissue ; however, in view of the low degree of 
accuracy obtainable with the colorimetric method used, and also in con- 
sideration of the variability of plant tissue, it is probable that this difference 
cannot be regarded as significant. 
It is a possibility that with discs of living tissue the dye is chiefly absorbed 
by the superficial dead cells, but examination of sections under the micro- 
scope showed that the dye penetrated to the internal living cells. 
5 . Effect of temperature. 
As only a few experiments were made to test the effect of temperature, 
no definite conclusions can be drawn. It is interesting to note, however, 
that the percentage absorption of the dye is increased with decrease of tem- 
perature ; this is especially marked in the case of the more dilute solutions. 
This effect of temperature is characteristic of adsorption processes as distinct 
from chemical combinations. 
O o 
