Permeability 143 
The method of de Vries (1885) of rendering visible the inner 
plasmatic membrane, by plasmolysing with 10 per cent, potassium 
nitrate and staining with eosin, is open to similar objection. 
In experiments on the penetration of a number of dyes into intact 
cells of a number of plant and animal species, and through the internal 
protoplasm of torn cells, Kite (1913 a, 1913 b, 1915) finds the surface 
layer of the cells he investigated is generally more easily penetrated 
by a dye than the interior protoplasm. So far, however, from 
regarding this as any evidence of the existence of a limiting plasmatic 
membrane, he speaks of such membranes as hypothetical structures. 
Although his results are in direct contradiction to the general opinion 
of the permeability properties of plasmatic membranes, it is not clear 
how he comes to regard such membranes as non-existent. 
(2) UUramicroscopic observations. The observations of Gaidukov 
and Price with dark-ground illumination have been referred to in 
Chapter II. Some of their observations relate to the plasma-mem¬ 
brane. 
Gaidukov (1910) records a differentiation between the outer layer 
of the cytoplasm and the internal part of the cell, but it is not clear 
from his description whether this outer layer can be referred to 
hyaloplasm or not. The observations of Price (1914) are more definite. 
In the cells of the leaf of Elodea canadensis “ no definite differentiation 
into endoplasm and ectoplasm was made out.” In the cells of the 
large multicellular hairs of the stems and leaves of Cucurbita spp. 
“ there is what appears to be a slight membrane limiting the protoplast 
towards the vacuole, and also forming the surfaces of the strands” 
(that is, of protoplasm). In the cells of the hairs of the tomato an 
outer layer of the cytoplasm appears to be differentiated from the 
rest of the cytoplasm, the particles in Brownian movement being 
smaller and less numerous than in the main mass of the proto¬ 
plasm. In a series of observations made on the germination of 
spores of a species of Mucor, the contents of the ungerminated spore 
appeared almost homogeneous, but after absorption of water had 
taken place for several hours a peripheral layer with the appear¬ 
ance usually attributed to a gel became differentiated from the 
general mass. 
Price also studied the appearance of plasmolysed cells under 
dark ground illumination. He states that in Spirogyra plasmolysed 
with dilute glycerol a layering of the protoplast can be observed, an 
external layer containing extremely fine particles becoming differ¬ 
entiated from the inner region containing the larger microsomes. 
