Frits ch . — The Moisture Relation of Terrestrial Algae. /. 19 
in the Horrnidium stage of Prasiola, but in all the terrestrial algae investi- 
gated is far smaller than in aquatic Algae. 
6. Terrestrial algae, therefore, and especially Pleurococcus , require 
only relatively small amounts of moisture to replace that lost by the proto- 
plast in drying. 
7. Appreciable amounts of moisture can be absorbed from the at- 
mosphere at times when the humidity of the air is great, and it is probable 
that a certain amount of growth can be effected during such periods. 
8. Terrestrial algae respond more rapidly to changes in the hygro- 
metric state of the air than does inanimate material. At times of low 
humidity they exhibit a more rapid falling off in the rate of loss of moisture 
than non-living material. 
9. The sap of the terrestrial algae investigated shows a high degree 
of concentration, which probably becomes so marked after a little evaporation 
has taken place that further loss of moisture is prevented. The rate of 
drying of the different forms, however, differs considerably, the Horrnidium 
stage of Prasiola taking longest to attain an air-dry condition. 
It thus appears that these terrestrial algae are well equipped for the 
vicissitudes which they have to face. Drying, in the sense in which the 
term could be applied to a flowering plant, does not take place, since 
the air-dry cells still contain in their protoplasts a considerable amount 
of moisture. This retention of moisture is presumably in great part due 
to the high concentration of the sap, although in view of the absence or 
paucity of obvious vacuoles it is possible that a large part of the sap is held 
adsorbed by colloidal constituents within the protoplast. The granules 
which are so characteristically produced as a reserve by all these terrestrial 
algae may be an expression of the peculiar conditions in the protoplasts 
as a result of the absence of vacuoles. Possibly, too, they form part of the 
mechanism by means of which moisture is retained in the cells. 
East London College, 
March , 1921. 
Literature cited. 
1. Bristol, B. M. (1919) : On the Retention of Vitality by Algae from old Stored Soils. New 
Phytol., xviii, 1919, p. 92. 
2. Chodat, R. (1902) : Algues vertes de la Suisse. Berne, 1902. 
3. FriTSCH, F. E. (1916) : The Morphology and Ecology of an Extreme Terrestrial Form of 
Zygnema ( Zygogonium ) ericetorum , (Kuetz.) Hansg. Ann. of Bot., xxx, 1916, p. 135. 
4. Gay, F. (1891) : Recherches sur le developpement et la classification de qtielques Algues vertes. 
Paris, 1891. 
