4 Fritsch . — The Moisture Relations of Terrestrial Algae. I. 
It will be noticed that in practically all cases drying proceeds at 
a considerable and fairly uniform rate until a large portion of the contained 
moisture has evaporated ; after that the amount of moisture lost on 
successive days exhibits a steady decrease to zero. When the second 
phase sets in, the materials appear dry to the eye, although still often 
damp to the touch. The first phase probably corresponds to the evapora- 
tion of moisture from between the particles or threads of material, whilst 
in the second we are dealing with the escape of moisture from the substance 
of the materials themselves. Drying takes place most rapidly in Clado- 
phora (8 days), Pleurococcus (9 days), and Zygnema ericetorum 
(10 days) ; next come Spirogyra (udays) 1 and the cotton-wool (11 and 
12 days respectively), whilst the Hormidium stage of Prasiola is the 
slowest of all the algae (15 and 16 days respectively). The clay soil 
employed had not yet dried completely at the end of the experiment 
(18 days). These data will be discussed more fully below (p. 14). 
It will be evident from a glance at Table I that the amount of moisture 
lost varies appreciably in the different materials. This is no doubt due 
both to a varying capacity for the absorption of liquid water and, to 
a minor extent (cf. below), to a varying power of retention of moisture on 
the part of the air-dry material. The relevant data are summarized in 
Table II. Pleurococcus exhibits by far the smallest moisture-holding 
Table II. 
Comparison of the amounts of moisture held by the different materials 
dealt with in Table I, in relation to volume and air-dry weight. 
Nature of material. 
Volume of 
same. 
c.c. 2 
Zygnema ericetorum 
3-5 
Hormidiwn stage ( Prasiola ) 
6-o 
» 5> 
5-5 
Pleurococcus 
1 i-o 
J9 
n-5 
Spirogyra 
1 -5 
Cladophora 
i*5 
Cotton-wool 
2-0 
5> )> 
2-0 
Soil 
10-0 
Moisture 
Ditto per 
Ratio of 
moisture 
lost. 
c.c . 2 
lost to air- 
grm. 
9-837 
2.8 
dry weight. 
4.6 
23-113 
3-8 
9-3 
17.241 
3 *i 
7.2 
3-783 
o -3 
0.6 
4-351 
0.3 
0.6 
12.645 
8.4 
20.3 
12.013 
8.0 
19.7 
22.304 
1 1 *4 
jo-8 
22.253 
IX. 1 
11.5 
9 - 7 11 
0.9 
0.4 
capacity (smaller even than that of the soil) among the algae studied, 
whilst the two freshwater algae have the largest ; the same volume of 
cotton-wool, however, exceeds them in absorptive capacity. It is quite 
clear from a study of the figures in the last column of Table II that in 
1 The slower rate of drying of Spirogyra as compared with Cladophora is no doubt due to the 
mucilaginous character of the walls. 
2 These data are only approximate. 
