566 Williams . — On the Influence of Immersion in certain 
been the case in the plants from another source used in the earlier work ; 
consequently in the K 2 Cr 2 0 7 tests a general appearance of precipitate 
was sought. 
It is important to record that no stirring was done during the 
immersions, and care was taken to remove sections at the necessary 
intervals with the least possible disturbance. 
The temperature of the thermostat was read at intervals and the 
usual fluctuation during an immersion was 1 per cent. ; in a few cases it 
amounted to 2 per cent. 
Observations upon the Nature of the Change. 
With a view to finding whether the change was of a reversible type, 
sections were closely examined after different stages of immersion and the 
following facts observed : 
(a) With concentrations of salts sufficient to cause ordinary plasmolysis 
the nature of the surface underwent changes as immersion was continued. 
At first the surfaces were parts of smooth curves with the exception of the 
threads connecting small spheres ; later, irregularities appeared and the 
protoplasm became more granular. 
(b) With the weaker solutions a shrinkage was very slowly induced, 
and here again the protoplasmic surfaces showed irregularities. 
(c) Circulation slowed down, and, in a thin section, had stopped in 
almost every cell at the stage when the reaction with the K 2 Cr 2 0 7 could 
be obtained. 
(d) Sections immersed for the critical times did not recover their 
circulatory power or normal appearance upon even prolonged treatment 
with distilled water. 
Further examination was carried out with the £ dark field ’ illumination 
produced by a paraboloid condenser. Material immersed for the critical 
times in KI or in KC1 was used in these tests. Before immersion the 
sections showed, against the black field, light scattered from their cell- 
walls and from chloroplastids, very faint light scattered from the general 
protoplasm, and some bright particles, difficult to focus, near the surface 
of the protoplasm. These particles possessed Brownian movement. 
With the same focus it was seen after immersion that movement had 
stopped, but there was much more general diffusion of light, denoting a state 
of greater aggregation. No further change was observed when the sections 
were left in distilled water. 
When the K 2 Cr 2 0 7 was applied, particles in Brownian movement 
appeared in the corners of the cells as well as in connexion with the 
plasmolysed masses. 
These facts, taken collectively, show that immersion for the critical 
time produces an irreversible change and the material may be said to be 
