386 MacDougal . — The Mechanism of 
must also be largely influenced by the degree of development 
of the mechanical tissues, and the elastic extensibility of the 
walls of the mobile tissues. In order to ascertain the con- 
ditions resulting in the active cells, tendrils of Passiflora 
which had been plasmolysed in 2, 3 and 4 per cent, solutions 
of potassium nitrate, .and allowed to remain in the solution 
until killed, were carefully hardened by the use of series of 
alcohol-mixtures and stained. In the parenchymatous tissues 
of both the concave and convex sides of the tendril, the cells 
were strongly plasmolysed, so that the protoplasts were in 
a large number of instances torn completely from the wall. 
The differences in form and size of the cells of the convex 
and concave sides make comparisons difficult, but it was 
apparent that the outer rows of parenchymatous cells of the 
concave side immediately internal to the collenchyma had 
lost their oblong ovoid form and become irregularly globoid. 
In these cells the ectoplasmic layer was barely separated from 
the wall, while in the cells of the convex side, whose walls 
retained their normal stature, the separation was quite distinct, 
and the protoplast enclosed no more than a half or two-thirds 
of the volume of the cell. The only satisfactory explanation 
of such conditions is that the solution, while it simply plas- 
molysed the cells of the convex side which retained their 
normal stature, acted as a stimulus on the contracted cells of 
the concave side, upon which the ectoplasm became extremely 
permeable to water and allowed the sap to escape. The 
elastically extended walls of the plasmolysed and mechanical 
tissues contracted simultaneously, indirectly causing the cur- 
vature of the tendril, immediately after immersion in the 
plasmolysing fluid. The solution afterwards penetrated the 
wall of the contracted cells sufficiently to slightly plas- 
molyse them. The continued curvature of the organs, when 
placed in distilled water, can only be due to conditions 
similar to those prevailing in loosely coiling mature tendrils, 
the most important feature of which is the loss of the power 
of growth and turgidity of the parenchymatous cells of the 
concave side. 
