710 Fritsch and Haines. — The Moisture-relations 
capacity of the cells to plasmolyse. This was shown by the fact that on 
May io a io per cent, sea-salt solution produced far more plasmolysis 
than a 5 per cent. one. The frequent failure to recover, or the slow recovery 
noted in many of our experiments, is no doubt to be ascribed to the fact 
that the intensity of the drought to which the material was subjected was 
in general rather great, probably far greater than ordinarily occurs in nature. 
That the difference between drought and wet material is not confined to the 
filamentous forms is illustrated by Fig. 6, which gives the results of experi¬ 
ments with Pleurococcus . 
The question may now be approached as to the actual nature of the 
change that takes place in the cells of the forms investigated during a period 
of drought. There are obviously various explanations that could be 
advanced to account for the gradual disappearance of the tendency to plas¬ 
molyse. Thus, there may be an increase in the permeability of the proto¬ 
plasts, production of additional osmotic material may take place, or the 
viscosity of the protoplasts may increase to such an extent that the latter 
become sufficiently rigid to resist the tendency to undergo contraction. In 
the case of recovery of material kept in hypertonic solutions there is the 
further possibility that the protoplasts are slightly permeable from the 
beginning, but this is unlikely to apply to more than a minority of the cells, 
in view of the persistence of plasmolysis in the majority in open hypertonic 
solutions. 
(a) Observations on Permeability to Stains. 
1. Zygogonium. In the case of Zygogoninm (material from habitat III) 
experiments have been conducted with a number of different stains, dis¬ 
solved in small quantity in a 5 per cent, solution of sea-salt, in order to 
investigate a possible relation between the penetration of the stain and the 
occurrence of plasmolysis. After treatment for twenty minutes with such 
a solution to which a little methyl violet had been added, the dead and 
unplasmolysed cells of the alga showed deep staining of the walls and 
the protoplasts, whilst in the plasmolysed cells the latter were practically 
unaffected. After five minutes in a 5 per cent, solution with four drops 
of aqueous 1 per cent, erythrosin the unaffected cells were deeply stained 
and the majority of the plasmolysed cells unstained ; treatment for half 
an hour afforded the same result, though the staining was much more 
pronounced. When a little eosin was dissolved in the plasmolysing solu¬ 
tion, only the unaffected cells were stained as a general rule ; the result was 
apparent already after five minutes, but much more marked after half an hour. 
On the other hand, methyl green, nigrosin, and Bismarck brown afforded 
no such results, even after an hour’s treatment; in the first two cases there 
was no evident penetration of the stain into any of the cells, whilst with 
Bismarck brown there was faint staining of the chloroplast in all cases. 
