144 
Walter Stiles 
The outer layer appears to be drawn out in places into threads which 
at their outer end retain contact with the cell wall. Such fibrils have 
frequently been recorded as occurring in plasmolysis (Gardiner, 1884; 
Bower, 1885; Chodat and Bourbier, 1898; Hecht, 1912). The particles 
in the outer region were in active movement, and there was no sign 
of a hydrogel layer limiting the protoplast, but Price suggests that 
some definite boundary must be present as the colloid particles do 
not escape into the surrounding liquid. Cells plasmolysed with 10 per 
cent, potassium nitrate presented a similar appearance. 
Sometimes during the plasmolysis of Spirogyra, vesicles of proto¬ 
plasm containing presumably cell sap are formed (cf. de Vries, 1885). 
The wall of the vesicle contains particles in active movement and if 
any part of the protoplasm is in the gel state it must be an extremely 
thin layer, for.none is obvious. In Mougeotia on the contrary, the 
wall of the vesicle appears to be rather in the gel condition. 
During plasmolysis of the cells of the hairs of Cucuvbita the 
protoplast appears to be bordered on the outside by a definite 
transparent membrane on which finer particles in the interior of the 
protoplast appear to impinge. This membrane was observed when 
plasmolysis was brought about by 30 per cent, sucrose, and so is 
presumably to be regarded as normal and not produced by the 
coagulating action of electrolytes. 
It is scarcely possible to draw any very definite conclusion from 
this work with regard to the general presence of a plasma-membrane. 
In the hairs of the tomato the outer layer differentiated from the rest 
of the cell contents appears to be identical with hyaloplasm; in the 
hairs of Cucuvbita there appears to be a thinner layer of a gel nature, 
limiting the protoplast on the outside. 
(3) Evidence from the results of microdissection. The observations 
made on the structure of protoplasm by means of microdissection 
have already been mentioned in Chapter II. The conclusions to which 
workers with this method come in regard to the plasma-membrane 
will now be indicated. 
Chambers (1917) describes the peripheral layer of the cytoplasm 
of young germ cells, egg cells and Protozoa as much denser than the 
interior cytoplasmic sol, but merging insensibly into it, and concludes 
that this surface layer is a highly extensile, contractile and viscous 
gel. If this surface layer is injured a new and similar layer will form 
at the damaged place, the capacity for the establishment and mainten¬ 
ance of the viscous gel layer being a property essential to cytoplasm. 
The rate of diffusion of three dyes, neutral red, cresyl blue and janus 
