688 
Fritsck and Haines.—Fhe Moisture-relations 
Pleurococcus , which in this respect proved to be as indifferent as to other 
treatment described later, the material grown in the dark showed a much 
larger percentage of plasmolysing cells. This, except in the Hormidium , 
is due to a great increase in the numbers of strongly plasmolysed 1 cells. 
The Zygogonium used was granular throughout, and remained so in both 
cases; that which had been kept in the dark, however, was found to present 
a majority of cells with very fine uniform granules, whilst the threads ex¬ 
posed to the light partly consisted of cells with large coarse granules. 
In the material that had been in the dark there were very occasional 
threads with relatively scanty granules, but on the whole one was struck 
by their apparent stability; if they constitute a food-reserve, they do not 
appear to be easily used during a prolonged period in which photo¬ 
synthesis is impossible (cf. Piercy, 1017 , p. 533). The Hormidium em¬ 
ployed contained relatively few granular cells, and here too there was 
no sensible alteration in this respect in either lot of material at the end 
of the experiment. The percentage of dead cells was considerably 
greater in the algal mats that had been in the dark. In the case of 
the protonema there was likewise no obvious difference in the micro¬ 
scopic characters of the two sets of material. 
Table III. 
Comparison of plasmolysis of identical material kept in the light 
and dark respectively (Expts. VIII and XXXVI). 
Materia^. 
Hormidium 
Protonema 
Pleurococcus 
(l. = light; d. = dark.) 
Cells 
Strength 
Time of 
counted. 
of sol. 
exposure 
0/ 
/o 
(days). 
90°, 971 
5 '° 
14*0 
1 ,022, I,o6o 
3 *° 
29*0 
1 ,000, 1,000 
5 '° 
25*0 
1,000, 1,000 
25.0 
14*0 
Strongly Slightly 
plasmolysed. plasmolysed. 
% % 
Unaffected. 
0/ 
/o 
d. 1 . d. 
69-3 12-5 227 
39' 1 4 2 '4 43’S 
75*3 387 1 9*4 
Plasmolysed. 
0/ 
/o 
l. 
437 
28*6 
d. 1 . 
8-0 44*0 
17-1 29-0 
2°-3 5-4 21*0 
Unaffected. 
% 
d. 
86*0 
/. 
82*5 
d. 
14*0 
l. 
17-5 
The results just given may be ascribed to two possible causes. 
The larger number of plasmolysing cells in material kept in the dark 
may be a result of decreased permeability of the protoplasmic membrane. 
At the same time it seems probable that the differences are partly caused 
by the presence of abundant soluble products of photosynthesis in the cell- 
sap, and that the frequent absence of plasmolysis in strongly granular cells 
is due to such cells being rich in products of assimilation. 
1 Cf. foot-note on p. 686. 
