714 Fritsch and Haines. — The Moisture-relations 
The result could be explained as due to a decrease in the permeability 
of the protoplasts, but this is not very likely in the face of other conclusions 
reached in the present paper. It seems more probable that it is to be 
ascribed to a change in the reaction of the protoplast, so that the stain is 
not accumulated. Evidence for this view is afforded by the fact that stains 
of opposite sign (eosin and erythrosin on the one hand, neutral red on the 
other) are respectively only capable of accumulation when the material is in 
a condition in which it is unaffected by the opposite stain. Zygogonium, as 
already mentioned, does not show this change in behaviour towards neutral 
red during drought, which is indicative of the diversity and complexity of 
the phenomena involved. Soaking of the drought material with water, as 
in Zygogonium , leads after some days to a recovery in the original direction 
(cf. series 2). 
3. Moss prolonema. Treatment of the original material of Experiment 
XV (cf. Table V) with 5 per cent, sea-salt, to which a very small quantity 
of eosin had been added, gave results analogous to those above described 
for Zygogonium. The vast majority of the unaffected cells were deeply 
stained, the slightly plasmolysed cells stained after a little time, and most of 
the strongly plasmolysed ones were unstained, although a few here and 
there were deeply coloured. The drought material of this experiment 
treated in the same way showed the majority of the unaffected cells unstained, 
the slightly plasmolysed ones mostly stained, whilst a few of the strongly 
plasmolysed cells were stained, though most of them were not. Since the 
statistical observations in Experiment XV (cf. p. 693) indicate that some at 
least of the originally strongly plasmolysed cells can recover, and since direct 
microscopic observation of protonema sealed in a 5 per cent, sea-salt solution 
(cf. pp. 703, 704) shows that some of these cells are incapable of recovery, it 
would appear that there are in the protonema used two types of strongly 
plasmolysing cells differing in their degree of permeability. Some are 
altogether impermeable and remain plasmolysed, others are slightly per¬ 
meable, so that, though plasmolysed at first, they ultimately recover. It 
should be emphasized that there does not appear to be any great difference 
in the behaviour towards eosin on the part of the strongly plasmolysed cells 
in the fresh and the drought material, the principal difference lying in the 
unaffected cells. 
Material that had been for four days in 5 per cent, sea-salt in a sealed 
slide (Experiment XXIII, Table IX) showed, after twenty minutes’ treatment 
as above, practically all the slightly plasmolysed cells stained, whilst the 
unaffected and strongly plasmolysed ones were each about half stained, half 
unstained (cf. wdth the results for drought material). In another experiment 
(XV, Table IX), with six days’ exposure to the solution, all the cells stained 
deeply in a short time, although some of the strongly plasmolysed ones 
more slowly than the others. 
