of Terrestrial Algae. II. 717 
as a result of the development of phycoporphyrin, whereas in the latter they 
were pure green. 
The only cells which after drought can be regarded as really healthy 
are those whose protoplast is quite uncontracted, which possess a healthy 
green colour, and in the filamentous algae usually have a very regular layer 
of fine, even granules at the periphery of the protoplast. These cells, which 
after prolonged drought are not very numerous or may be completely 
absent, are the ones which prove to be impermeable to eosin in the case of 
Zygogonium (cf. p. 712) and the protonema (p. 714), whilst the slightly con¬ 
tracted cells are all readily permeable, although not generally as rapidly as 
the dead cells. 
In the case of material kept in hypertonic solutions (cf. p. 70 6 et seq.) 
there are likewise usually a certain number of cells with uncontracted pro¬ 
toplasts, and, from the similarity in microscopic characteristics, it is probable 
that they are the same cells as appear quite unaffected at the end of a drought 
experiment. Side by side with the unaffected cells in material kept in 
hypertonic solutions there are, however, far more numerous strongly plas- 
molysed cells. Some at least, if not the majority, of these must correspond 
to the numerous cells with permanent slight contraction of the protoplast in 
drought material. These cells are therefore more resistant to a prolonged 
sojourn in a hypertonic solution than to drought, since the great permeability 
of these cells in the latter case probably an indication of their being in 
a more or less unhealthy condition, leading sooner or later to death, and from 
which a recovery is perhaps only possible in early stages (cf. p. 7c6). More¬ 
over, although plasmolysed, the protoplasts of the cells in open hypertonic 
solutions are not rigid, since they recover in tap-water (cf. p. 707). 
The healthy uncontracted cells remaining after drought and prolonged 
treatment with hypertonic solutions, in view of their practical impermeability 
to stains, are probably also impermeable to the salt solution. Since they 
remain unplasmolysed, the concentration of their sap in osmotic material 
would seem to be at least as great as that of the 5 per cent, sea-salt solution 
used. In fresh material, however (cf. Table XIV), it is the plasmolysed and 
not the unaffected cells that fail to take up stains. To account for the 
presence of unplasmolysed and non-staining cells in the final condition, 
therefore, there are two possible explanations: These cells may be the 
unaffected ones of the original material (which might be supposed to have 
an osmotic strength greater than 5 per cent, sea-salt solution) which, at first 
readily permeable, have become impermeable. Alternatively these cells may 
be the original strongly plasmolysed ones which have remained relatively 
impermeable but have met the conditions to which they have been subjected 
by the formation of additional osmotic material. The failure of both 
suggestions to cover the facts completely, since the cells in question are 
often also unaffected by solutions far stronger than 5 per cent., hints at the 
