727 
of Terrestrial Algae. II 
be more or less impaired. At the same time the fact that the really 
healthy surviving cells are apparently always those that are provided with 
fine peripheral granules of unknown nature hints at the probability of still 
other factors coming into play. It is not impossible that moisture-retention 
may be partly due to a change in the cell-walls, since alterations in staining 
reactions, sometimes shown by the walls during drought (cf. p. 712), indicate 
that they also are capable of some modification under these conditions. 
H. Summary. 
The present paper deals with the changes occurring in terrestrial algae 
and moss protonema during drought and when exposed for long periods to 
hypertonic solutions. During drought there is a gradual diminution in the 
tendency of the cells to plasmolyse with a given hypertonic solution until 
finally there is no appreciable plasmolysis at all. At the same time there 
is a marked alteration in the permeability of the cells to stains. Sub¬ 
sequent access of moisture brings about changes in the reverse direction, 
unless the drought is severe or very prolonged. If material is sealed in 
a hypertonic solution and investigated day by day, a similar gradual dis¬ 
appearance of plasmolysis is noted, an effect which is probably partly patho¬ 
logical. In all these respects, however, Pleiirococcus shows far less tendency 
to change than the filamentous forms examined. 
In material exposed to hypertonic solutions, but unsealed, only a certain 
number of the cells recover from plasmolysis and the majority of these sub¬ 
sequently die ; the rest, often a large percentage, remain plasmolysed, though 
retaining their vitality for weeks or months. At the same time there is 
usually a small number of healthy cells with uncontracted protoplasts. 
The cells surviving after a period of drought or of prolonged treatment 
with hypertonic solutions have a moreorless rigid, highly viscous protoplast 
without obvious vacuoles. This has been demonstrated especially by the 
use of dark-ground illumination and the examination of ‘ centrifugalized ’ 
material ; it is the normal state of the cells of Plenrococcits and Prasiola. 
It is suggested that this gel-condition of the protoplast may in part explain 
the marked retention of moisture by such terrestrial forms in the air-dry 
condition, although there are some indications that other factors also are 
concerned. 
East London College, 
March 22, 1923. 
