of Terrestrial Algae . II. 711 
A solution made up of one drop of 1 percent. Congo red in 1 c.c. 5 per cent, 
sea-salt produced a very deep coloration of the wall after three-quarters of 
an hour in all the dead cells, but only a very slight one, if any, in the living 
cells ; there was no penetration into the protoplast of the latter whether 
plasmolysed or not. It may be added that neutral red does not differentiate 
between different cells of this alga, as it does in Hormidium (cf. below) ; the 
stain is taken up very rapidly, even from a very dilute solution, and appears 
in the chloroplasts, which become deeply tinted. 
The cells of Zygogonium are thus permeable to different stains and, in 
the case of several of these, the degree of permeability varies, the stain 
penetrating readily into some of the cells and not into others. Eosin, as 
giving the most pronounced results and apparently not staining the wall, 
was selected for further investigations. The number of cells becoming 
stained after half an hour’s treatment differs very much (cf. the first column 
of Table XV) and evidently depends on the condition of the material. 
Table XIV. 
Relation between penetration of eosin and response to 5 per cent, sea-salt 
solution on the part of fresh material of Zygogonium} 
(Habitat II, Experiment XXV.) 
Strongly plasmolysed. Slightly plasmolysed. Unaffected. 
r 
Stained. 
°/ 
Unstained. 
c / 
Stained. 
Unstained. 
0/ 
Stained. 
C/ 
Unstained. 
O/ 
Vo 
Immediately 3-2 
Vo 
35 -o 
Vo 
9.2 
Vo 
33-6 
/o 
19-0 
Vo 
After one hour 15-4 
2-1 
42*1 
37*9 
— 
The rate of penetration of the stain varies. In Experiment XXV (cf. 
Table XIV) the unaffected cells stained immediately, and so did some of the 
plasmolysed ones. The majority of these, however, required a varying time 
to take up the stain, but it had penetrated into most of them at the end of 
an hour. This was, however, an extreme result, partly due perhaps to the 
experiment being performed in a very warm room, and in other cases many 
of the cells resisted the penetration of the stain for a much longer time. There 
is often, as mentioned above, a considerable degree of parallelism between the 
permeability to the stain and to a 5 per cent, sea-salt solution, as indicated by 
the occurrence or non-occurrence of plasmolysis. It may be pointed out, 
however, that the degree of correspondence between the two sets of pheno¬ 
mena will of course depend on the strength of plasmolysing solution used 
and the condition of the material. Threads which had been for a few days 
immersed in 5 per cent, salt solution (cf. p. 706) gave very definite results, 
1 Slightly over 200 cells counted at each estimation. Since the experiment was performed in a 
very warm room the material shows recovery at the second estimation. 
