705 
of Terrestrial Algae. II. 
recovery, if recovery is to occur at all. Another fact of some interest is that 
the extent of the initial plasmolysis bears no relation to the occurrence or 
non-occurrence of a subsequent recovery, nor to the rapidity with which the 
latter sets in. There are indications that recovery does not so easily take 
place in a 5 per cent, sodium chloride as in the balanced solution. Attention 
should finally be drawn to the fact that the conclusions detailed in the pre¬ 
ceding paragraph were drawn from a much larger number of observations 
than are shown in Table XI, which would have become too unwieldy if all 
had been included. 
Some rather peculiar results were obtained in analogous experiments in 
which sugars were used. If threads of Zygogonium are placed in a 20 per 
cent, sucrose solution, no plasmolysis at all is to be observed at first, although 
such a solution has an osmotic pressure exceeding that of a 3 per cent, sea- 
salt solution which plasmolyses many of the cells of the alga. A day later, 
however, slight plasmolysis is to be seen in many of the cells and remains 
apparent for some days, though ultimately mostly disappearing. The same 
results were obtained with 10 per cent, glucose, whilst 30 per cent, glucose 
causes immediate violent plasmolysis, from which the cells in a sealed slide 
recover in about two days. This matter has so far not been further 
followed up. 
In most of the cases described above, in which recovery was established 
by direct microscopic observation, a more or less marked central aggre¬ 
gation of the chloroplast or chloroplasts, as well as of the granules when 
present, was noted, the whole periphery of the newly expanded protoplast 
appearing clear, opaque, and whitish. Frequently, too, a change in the 
character of the granules was established, those in the final condition being 
large and irregular (cf. p. 716 on condition of the cells during drought). On 
the whole this condition was more evidently seen when recovery was rapid 
than when it was slow. 
It is probable that recovery from plasmolysis in a sealed slide is partly 
to be regarded as a pathological phenomenon, implying a state of decreased 
vitality on the part of the material, chiefly perhaps as a result of interference 
with respiration. There are two possible methods by which such a patho¬ 
logical condition could lead to the observed recovery. Firstly, it might be 
expected to bring about increased permeability of the cells, thus allowing 
penetration of the surrounding solution. Secondly, the protoplast might 
swell by simple imbibition, this process being augmented by degradation- 
products such as acids produced as a result of the unhealthy condition of 
the cell. Emphasis must, however, be laid upon the fact that, if such 
factors come into play, their action is different in the case of terrestrial and 
aquatic algae and also different in the moss and the flowering plant (cf. 
p. 703). Moreover, the very marked similarity in the response to drought 
and in the reaction to a continued exposure to the plasmolysing solution, 
3 A 2 
