722 
Fritsch and Haines.—The Moisture-relations 
moss protonema. Some of the cells become strongly plasmolysed, others 
only slightly, whilst a varying percentage are totally unaffected. In order 
to bring about plasmolysis of a majority of the cells, very high concen¬ 
trations are often necessary, the outstanding forms in this respect being 
Prasiola, Pleurococcus , and Cystococcus. With the latter two even 25 per 
cent, solutions of sea-salt leave about 10-20 per cent, of the cells unplasmo- 
lysed. In both of these respects aquatic algae afford a marked contrast, the 
cells plasmolysing with low strengths of solution and usually showing an 
almost uniform reaction. 
2. With increasing concentrations of sea-salt solution there is a progres¬ 
sive increase, both in the numbers of cells plasmolysed and in the extent of 
plasmolysis in the individual cells, a fact which implies that in the terrestrial 
forms investigated there is a more or less complete grading of the cells as 
regards their response to plasmolysing solutions. 
3. When subjected to concentrations not far above the minimum, the 
majority of the plasmolysed cells are those which lack the granules which 
are so characteristic of terrestrial algae, whilst with high concentrations the 
unaffected cells are almost invariably such as are rich in these granules. 
The granular or non-granular character of the cell is, however, not the only 
determinant of its plasmolysing qualities, as shown by the fact that far more 
plasmolysed cells are to be found in material grown for some days in the 
dark than in similar material that has remained exposed to the light. 
4. During a period of drought there is a progressive daily decrease in 
the degree of plasmolysis in the filamentous forms, as well as in the numbers 
of plasmolysed cells, culminating after some little time, as a general rule, in 
a complete absence of strongly plasmolysed cells and a majority of unaffected 
cells. There is thus evidently a gradual loss of the tendency of the cells to 
plasmolyse. 
5. In Pleurococcus (probably also Cystococcus ), on the other hand, there 
is no such definite response to drought. If the plasmolysing tendencies of 
the cells change at all, they do so only after very prolonged and intensive 
drought, and apparently death cf the cells may often intervene before any 
decisive response has occurred. In our numerous experiments with Pleuro¬ 
coccus very erratic, fluctuating results have been obtained which are at pre¬ 
sent inexplicable. 
6. If threads of the filamentous forms are permanently mounted in sea- 
salt solutions of varying strength in a sealed slide (cf. p. 689), the cells show 
a recovery from plasmolysis which is rapid at first, but subsequently slower, 
until after some days no decided plasmolysis is to be found. This fact has 
been established both by means of comparative estimations and direct 
microscopic observation. The rate of recovery depends on the temperature. 
7. If material of Pleurococcus or Cystococcus is sealed in this way in 
a 25 per cent, sea-salt solution, there is often no change for several days. 
