220 
Walter Stiles 
With these prefatory remarks we are now in a better position to 
consider some of the theories of cell permeability. 
The Ultrafiltration Theory 
The ultrafiltration theory of cell permeability appears to be a 
direct application to the cell of the sieve theory of membrane per¬ 
meability. In its present form it is founded on the work of Kiister 
(19x1) and Ruhland (1912, 1913 a, b, c, 1914) on the staining of 
various plant cells by a considerable number of dyes. The method 
chiefly employed was introduced by Kiister and consists in placing 
the cut surface of shoots in a solution of dye so that the solution is 
carried through the vascular bundles from which the dye, if it is 
capable of penetrating living cells, will pass into the latter. Using 
this method Ruhland examined the penetration of 89 acid dyes, 
chiefly into the tissues of young plants of Vida Faba, and came to 
the conclusion that a complete parallelism exists between pene¬ 
trability and diffusivity of the dye, the latter being examined by 
following the diffusion of the dye through a gelatin gel. The diffusivity 
is supposed to run parallel to the degree of dispersion (cf. Chapter iv), 
whence it is concluded that with acid dyes the capacity of penetrating 
into plant cells depends entirely on the degree of dispersion of the dye. 
Ruhland also examined the intake of 30 basic dyes by epidermal 
cells of the bulb scales of Allium Cep a and by cells of Spirogyra, and 
found that of these a few, namely, Victoria blue R and B, Basler 
blue R and BB, gallamin blue and night blue, were not absorbed, 
while two others, diazine green and Victoria blue R, were only 
absorbed slowly. All these dyes were also found to diffuse slowly 
through a gelatin gel. 
In some cases the intake of acid dyes by cells of the bulb scales 
of Allium Cepa and of the pith of the stalk of Helianthus annuus 
could be made plain after immersion of the tissue in the dye by 
plasmolysing with a strongly hypertonic solution of sugar or a salt 
so that a big contraction of the protoplast resulted, with a consequent 
intensification of the colour. Kiister (1918) has also obtained similar 
results in regard to the intake of acid dyes (acid fuchsin, light green 
FS and orange U) by cells of the pith of Coleus hybridus. 
The fact that basic dyes accumulate much faster than acid dyes 
is regarded by Ruhland as not related to permeability, but to be due 
to the combination of basic dyes with tannic acid (cf. Chapter xi) 
so that a considerable apparent difference in concentration of the 
dye on the two sides of the plasma-membrane is maintained. 
