PROTOPLASM THROUGH THE WALLS OF VEGETABLE CELLS. 
857 
plasmolysing such a cell as Tamus communis (Plate 70, fig. 33). In concluding the 
subject I should like to state nay views as to the reason why plasmolysis does not 
give any reliable assistance to the subject of the perforation of the cell-wall by 
protoplasmic threads. 
When the protoplasm separates from the cell-wall in consequence of the action of 
dehydrating agents, it always tends to assume a spheroidal form, in consequence of 
the action of the two forces of pressure and tension, which endeavour to bring about a 
state of equilibrium. Now the pulling force that the living protoplasm must exhibit 
in contracting from the cell wall and assuming its spheroidal condition must be very 
considerable. As we have seen from the appearance presented by such sections as 
Plate 70, fig. 40, there is a tendency on separation for the protoplasm to adhere 
rather to the main protoplasmic mass than to the cell-wall, and in consequence 
of this the protoplasm of the fine filaments goiug through the cell-wall will tend to 
be pulled out of its canal, and thus the thread proceeding from it will be no thicker 
than one which arises from the general cell-wall, and will therefore not be especially 
apparent. In instances where plasmolysis is very rapidly induced, the protoplasm 
quickly contracts, and even becomes divided up into several masses. Then if may 
possibly happen that, owing to the particular combination of forces, a minute sphere 
of protoplasm may be retained, sticking to the pit membrane (as in Plate 70, fig. 34), 
although it may equally well adhere to the cell-wall (as in Plate 70, fig. 35). 
But with such strong reagents as sulphuric acid the case is different. Owing to 
the rapid death of the pi-otoplasm, the assumption of that spheroidal form attended 
with the exhibition of the usual rending force between the protoplasm and the cell- 
wall is prevented. The factor of life no longer asserts itself, and the contraction 
produced is now merely a mechanical shrinking, in consequence of dehydration, and 
the separation tends to take place rather between protoplasm and cell-wall than 
between protoplasm and protoplasm. Thus any intimate union which may exist 
between the protoplasm of the cell and the protoplasm running through the cell-wall 
tends to be maintained, and if sufficiently pronounced is made evident.'" 
I am now in a position to bring my paper to a conclusion. 
I have succeeded in demonstrating that in living tissues a means of communicatioD 
between adjacent cells exists. My results have been confirmed by Russow, whose 
valuable contribution I have already mentioned. The wide field that this discovery 
opens is so great, and the whole bearing of the subject is so enormous, that it 
would be useless for me either to attempt to sketch its significance or indicate 
the important inferences which arise therefrom, in the present paper. We are now 
in a position if not to understand, at least to get a clearer insight into, such phenomena 
as the downward movement of a sensitive leaf upon stimulation, of the wonderful 
action of a germinating embryo on the endosperm cells, even those which are far 
* In connexion with this subject, see De Baby’s figure of the sieve-tube of Vitis after the action of 
iodine and potassic iodide ( loc. cit., fig. 75, p. 186). 
