7i5 
of Terrestrial Algae. II. 
Two separate investigations (Experiment XXXIII) on the progressive 
changes in staining of the cells of protonema with eosin during drought 
( 34*5 P er cent, sulphuric acid in the dark at i8° C.) have been undertaken. 1 
In the first series the percentages of stained cells on successive days were: 
17-5 (original material), 20*3, (87.5,18-5,17-2 ; in the second series they were : 
29*4 (original material), 38-7, 99-8, and, after four days’ drought, approxi¬ 
mately half the cells stained (actual count not made). In both series the 
result, for the first two days of drought, was as in Zygogonium , but after that 
there was in each case a great decrease in the percentage of stained cells, 
a fact for which there is at present no satisfactory explanation. In the 
second series parts of the protonema mat were removed at various stages of 
drought and soaked with water, though otherwise left under the same con¬ 
ditions. Material thus removed after two days’ drought (then showing 
99-8 per cent, cells stained) gave one day after soaking 81-7 per cent, and 
two days after soaking 79-3 percent, stained cells, after three days’ drought 
and one day’s soaking with water 86-4 per cent, stained cells. It is evident, 
therefore, that with reference to the capacity to exclude the stain there is 
very little recovery on the part of drought material in this case. Only one 
investigation of the effect of dilute erythrosin has been undertaken, and this 
afforded results which were practically identical with those obtained with 
Hormidium and Zygogonium ; after five days’ drought the majority of the 
cells stained deeply in a short space of time. 
4. Pleurococcus and Cystococcus. No clear results have been obtained 
with either of these algae. If cells of Pleurococcus are mounted in 0-2 per 
cent, eosin, only very few take up the stain, and simultaneous treatment 
with a 25 per cent, sea-salt solution shows that the strongly plasmolysed 
cells never stain, the dead cells invariably, whilst of the unaffected cells 
roughly half are stained. Nor is there any sensible difference in drought 
material ; thus, in Experiment XXX (cf. Table V) an estimation, made after 
ten weeks’ drought, showed that only 6-4 per cent, of the cells stained, which 
corresponds to about one-third of the unaffected cells present. In the same 
experiment, material that had been subjected to four weeks’ drought and had 
then been soaked with water for six weeks gave 6-o per cent, cells stained, 
corresponding to about one-half the unaffected cells. Examination of 
material which had been in a 25 per cent, solution in a sealed slide for seven 
days (Experiment XVII, Table IX) afforded identical results, the ratio of 
stained to unstained unaffected cells being 41 : 59. In the case of Cystococcus 
the unaffected cells on the whole stain more strongly with eosin than the 
plasmolysed ones, but this is not an invariable rule. No difference could 
be detected in this respect between fresh and drought material. 
The general conclusions to be drawn from the above observations are 
considered in the next section. 
1 Method as above described for Zygogonium ; 1,000 cells or more counted at each estimation. 
