1 6 Fritsch. — The Moisture Relation of Terrestrial Algae. /. 
one-half of it is permanently lost, and it is probably justifiable to assume 
that some of this at least represents moisture that was retained by the 
living protoplasts and is incapable of being reabsorbed by them when dead. 
The considerable range exhibited by the figures in the last column of 
Table VI is probably in part due to the varying purity of the material ; 
it is very difficult to get rid of all soil and other intermingled matter. 
Moreover, the air-dry weight depends on the hygrometric state of the air 
on the day of the experiment. A range between 25 and 35 is probably 
the normal for this alga. 
In Table VII the results of similar experiments with air-dry material 
of the different forms discussed in this paper are given for comparison 
with one another and with freshwater algae, cotton-wool, and soil. The 
materials are the same as those dealt with in Tables I and II. 
Table VII. 
Determination of dry weight and of amount of moisture permanently lost 
on heating of various materials. 
Nature of 
material. 
Air- dry 
weight 
of same. 
Dry 
weight 
of same. 
Moisture 
lost. 
Ditto in 
% of dry 
weight. 
Weight 
after 
exposure 
to air. 
Perma- 
nent 
loss. 
Ditto in 
%of 
total 
loss. 
grm. 
grm. 
grm. 
grm. 
grm. 
Zygnema 
2.136 
1.942 
0,1 94 
9.9 
2.112 
0-024 
12.4 
Hormidium 
2.479 
2.234 
0-245 
10.9 
2.422 
o-o57 
23-3 
2-385 
2-190 
0195 
8.9 
2-336 
0049 
25.1 
Pleurococcus 
6-121 
5-753 
0.368 
6.4 
5.989 
0-132 
35-9 
n 
7-060 
6-737 
0-323 
4-8 
6-959 
O.IOI 
3 I *3 
Spirogyra 
0-620 
0-553 
0.067 
12. r 
o-6i8 
0-002 
3-° 
Cladophora 1 
o-6 t 3 
0.540 
0.073 
13-5 
0-607 
0.006 
8.2 
Cotton-wool 
2.065 
1.900 
0-165 
8.7 
2.041 
O.O24 
14-5 
>> >> 
I *94 1 
1 .811 
0.130 
7.2 
1.932 
0009 
7 -o 
Soil 
24.241 
23.702 
0-539 
2-3 
24.054 
O.187 
34-7 
On the whole these results are quite in harmony with the conclusions 
arrived at in the preceding sections. It is to be noticed that, by comparison 
with its dry weight, Pleurococcus exhibits the lowest percentage loss of 
moisture on heating of all the algal forms studied, so that it seems probable 
that the amount of moisture held by the air-dry cells of this alga is small 
(cf. above, p. 14). On the other hand, Pleurococcus shows the highest 
permanent loss (viz. 35-9 and 31-3 per cent, of the total) among the algae 
investigated in this experiment, although the Hormidium stage may exhibit 
a similar high value (cf. Table VI). It is legitimate to assume that 
most, at least, of the permanent loss observed in the case of Pleurococcus 
is due to inability of the dead protoplasts to take up the moisture formerly 
held ; in other words, that relative to the total amount of moisture retained 
by the air-dry alga that contained within the protoplast constitutes a large 
1 A certain amount of a narrow species of Oedogonium also present. 
