8 Fritsch . — -The Moisture Relations of Terrestriat Algae. 1. 
weeks) in winter should be approximately the same as in summer, since the 
range in percentage humidity of the air is about the same, but the data at 
present obtained indicate a smaller range in winter than in summer. On 
the other hand, the second relation recorded by Trouton and Pool was 
frequently observed, viz. that there is a much greater reduction in weight 
for a given change in vapour pressure when near saturation than is 
subsequently obtained. 
The phenomena referred to in the preceding paragraphs of this section 
are of course to be observed in all hygroscopic materials and are a result 
of adsorption and imbibition. In the case of material composed of living 
plant-cells, however, it would seem probable that moisture imbibed by the 
cell- wall would tend to become absorbed by the protoplast (cf. below, p. 13), 
so that moisture would be taken up more rapidly than in the case of 
inanimate material. Indeed, if one compares living with dead material 
a difference is very obvious (cf. Table V and Fig. 1). It will be noticed 
that the alga corresponds much more markedly with changes in the 
Table V. 
Comparison of change in moisture-content of the same area of powdered 
soil and Pleurococcus naegelii in relation to atmospheric humidity 
(increase indicated by + , decrease by — ; in all cases the increments 
are 
expressed in 
percentages of 
the total range observed during the 
period of the experiment, cf. foot- 
■note on p. 6 ). 
Date 
and hour } 
Soil . 
Pleurococcus . 
Hygrometer 
reading . 
Total range : 
Total range : 
0-243 grm. 
0-164 grm. 
Sept. 
6, 8.15 a.m. 
+ 6 9 | 
+ 7o* 
84.5 
j» 
6, 2 p.m. 
- 46 ^ 
-69J 
68 
99 
6, 8.15 p.m. 
4- II 
73 
99 
7, 8.20 a.m. 
+ 54 
+ 62 1 
84-5 
99 
7, 11 a.m. 
- 37 * 
— 61 
70 
99 
7, 12.30 p.m. 
-39 
58 
99 
7 , 5-i5 P- m - 
— 
+ iof 
65 
99 
7, 8.50 p.m. 
+ 12 
+ 17 
74 
99 
8, 8.20 a.m. 
+ 47* 
+ 47 
82 
yy 
8, 10 a.m. 
-a* 
-8 
82 
99 
8, 12.25 p.m. 
-26f 
~ 39 . 
67 
99 
8, 2 p.m. 
-17* 
-Mi 
66 
99 
8, 3.30 p m. 
“ 4 * 
+ 1 
66 
99 
8, 5 p.m. 
4 
5 
5 
“8 
66 
99 
8,. 7.30 p.m. 
+ 5 
+ 9 * 
7i 
99 
8, 8.55 p.m. 
+ 9 
+ 17 
75-5 
99 
9, 8.15 a.m. 
+ 33 | 
. +42 
85-5 
99 
9, 9.30 a.m. 
+ 2 
+ U 
86.5 
99 
9, 10.45 a.m. 
5 
— 6f 
84 
99 
9, 2.5 p.m. 
- 55 * 
-66* 
63 
99 
9, 5.25 p.m. 
-I 5 l 
— 9 * 
56 
99 
9, 6.25 p.m. 
+ 5 t 
+ 6| 
64 
99 
9, 8.15 p.m. 
+ 1 3 § 
+ 18* 
75 
99 
10, 8.15 a.m. 
+ 54 
4 - 68 * 
86 
1 Summer time. 
