621 
by the Method of Dark-ground Illumination . 
a definite membrane is strengthened by the fact that the colloid particles, 
although bombarding the surface, do not escape and produce a new colloid 
sol with the water. It is a significant fact that the figure is drawn from a 
case of plasmolysis in cane sugar, and unless water is to be regarded as 
sufficiently dissociated to cause coagulation of the sol on the surface, the 
presence of this membrane or ‘ Schicht ’ seems to be normal, and not 
produced by plasmolysis. 
PL XLII, Fig. 3, shows another case of plasmolysis of Cucurbita with 
30 per cent, cane sugar ; vesicular structures have been produced some- 
what like those in Spirogyra . These vesicles are composed of a very thin 
membrane, in which very fine scattered particles are seen to be moving. 
There seem to be vesicles within a larger one. Sap particles are enclosed, 
but are in this type of material comparatively few in number. 
The characters of the membrane rather distinguish it from the general 
mass of the protoplast. The plasmolysis here was performed with a non- 
electrolyte, and the membrane of the vesicle seems to be produced just as 
in the case of plasmolysis by electrolytes. 
The phenomena of plasmolysis have been briefly described for some of 
the more typical cases. No marked difference can be said to have been 
observed with different types of reagents, electrolytes, and non- electrolytes, 
those which penetrate the protoplast slowly, and those which cause more 
perfect plasmolysis. 
The description of the formation of' the protoplasmic fibrils, already 
casually mentioned, is reserved for another section. 
(b) The Protoplasmic Fibrils. 
In certain cases of plasmolysis, described by numerous investigators. 
Bower (’83), Gardiner (’84), Chodat et Bourbier (’98), and more recently 
studied by Hecht (T2), the contracted protoplast remains attached to the 
cell-wall by fine threads or fibrils of protoplasm. These fibrils vary in 
size and number, and were at one time thought to be continuous with the 
protoplasmic connexions through the cell-wall, and especially were they 
thought (Kohl, ’91) to indicate the presence of connexions through the 
cross walls of certain filamentous Algae. This view was, however, dis- 
proved, in part at any rate, by Chodat et Bourbier (see also Strasburger, ’01), 
and it appears that these fibrils represent nothing more than fine strings 
adhering to the cell-wall by their viscosity. 
These fibrils have been well observed by methods of dark-ground 
illumination, and some further facts concerning their nature and structure 
have been noted. They appear, when thus illuminated, as bright lines 
stretching from the cell-wall to the contracted protoplast. They are often 
extremely fine, so much so that at times they are not distinguishable in 
illumination by transmitted light. It thus seems probable that previous 
