of Terrestrial Algae . II. 723 
The data given in this paper indicate that at certain times these two algae 
are capable of remaining unaffected for a long time by the unfavourable 
conditions prevailing in such a sealed slide. 
8. The recovery referred to in 6 and 7 is probably in part pathological, 
but emphasis must be laid on the similarity of the response to that observed 
during drought, and on the fact that aquatic algae, as well as the epidermal 
cells of Saxifraga sarmentosa , show a very much smaller capacity for 
recovery under such conditions. The cells of the protonema and leaves of 
mosses seem in this respect to occupy a somewhat intermediate position. 
9. If small patches of soil bearing mats of the filamentous forms are 
placed in open vessels containing various concentrations of sea-salt (usually 
5 per cent.), a large number of the cells remain alive for weeks or even 
months. In the first days after such treatment a considerable number of the 
cells recover from plasmolysis, but the majority of these at least die within 
a week or so. The remainder are of a healthy green colour, but usually 
most of them are plasmolysed, though not very strongly. Even after weeks 
of the treatment these cells recover instantaneously if the threads are 
mounted in tap-water. Side by side with the plasmolysed cells there are 
always to be found a smaller or larger number of cells with quite uncon¬ 
tracted, healthy green protoplasts. Such might serve as the starting-points 
for growth, which has, however, vSO far been observed in one case only 
( Zygogonium ). 
10. Recovery from the effects of drought on subsequent access of mois¬ 
ture takes place only very slowly, unless the previous drought has been of 
short duration or relatively mild. In Pleurococcus it appears to be more 
rapid than in the others (cf. Fig. 6). 
11. The cells of the forms studied show marked differences among one 
another in their degree of permeability to certain stains. In the case of 
Hormidium treated with neutral red some cells are altogether unstained, 
others exhibit staining of the protoplasts except for the chloroplasts, whilst 
in a third group the entire contents are stained. 
12. In Zygogonium and the protonema the permeability to eosin (and 
other stains) runs more or less parallel with the behaviour of the cells 
towards a 5 per cent, sea-salt solution, the majority of the unaffected cells 
staining almost immediately, whilst the plasmolysed ones remain unstained 
for a much longer time. In Pleurococcus only the unaffected cells (using 25 
per cent, sea-salt solution) take up the stain, and only about half of these. 
13. During the progressive stages of drought a great increase in the 
permeability of the cells of Zygogonium , Hormidium , and the protonema to 
various stains is observable, the number of stained cells ultimately reaching 
nearly too per cent., although subsequently falling off again in an inexpli¬ 
cable manner in the protonema (cf. p. 715). In the final drought condition of 
the algae the only unstained cells are the few perfectly healthy ones. If the 
