1 48 Frit sch. — The Morphology and Ecology of an Extreme 
Two other features are generally cited as characteristic of the terrestrial 
form, viz. the frequent swollen shape of the cells and the formation of short 
rhizoids (Borge, T 3 , p. 37 ; Collins, ’ 09 , p. 120). As regards the first point, 
I have been unable to find any marked difference between the three forms 
in the shape of the cell, which varies between cylindrical and somewhat 
barrel-shaped. The rhizoids, which may be uni- or multicellular (Fig. 3, b), 
have been encountered only in the two terrestrial forms. 
To raise once again the question of the possibility of the Hindhead 
Alga being a separate species, it may be pointed out that, except for the 
chloroplasts, all the distinctive features appear merely as intensifications of 
the characters of the ordinary terrestrial form. As for the chloroplasts, the 
greater degree of independence of the two halves may be a result of the 
very slow growth of the Hindhead form and the consequent long intervals 
between successive cell-divisions. In short, I am inclined to regard the 
Hindhead Alga merely as a very extreme xerophytic form of Zygnema 
ericetorum . 
E. Summary. 
An extreme terrestrial Alga is described, probably belonging to 
Zygnema ericetorum and owing its peculiarities to the extremely inhospitable 
habitat on the Hindhead Common. The mature cell of this form contains 
two chloroplasts, much like those of other species of Zygnema , although 
they may hang together by an exceedingly narrow connecting bridge. For 
some time after division but a single chloroplast is found in each daughter- 
cell. Division is accomplished by the gradual invagination of the innermost 
layer of the cell-wall, but it appears that the septum thus formed is not 
completed for some time, a central pore remaining through which the 
daughter-protoplasts stand in connexion with one another. Two or three 
layers are distinguishable in the longitudinal walls. 
The Hindhead Alga may be said to be permanently in the akinete 
condition, its cells agreeing in many respects with the akinetes of such 
forms as iC leiospermunt , zT. pectinatum , &c. The outer portion of the wall 
is strongly thickened and mucilaginous, and is shown to play a great part 
in protecting the cells during periods of drought and in bringing about 
a rapid recovery on the reappearance of favourable conditions. The cells 
contain numerous fat-globules (Fig. 2, D), which, on the commencement of 
desiccation, form an exceedingly dense layer closely apposed to the inner 
surface of the membrane (Fig. 2, E, e') ; the function of these globules is not 
exactly clear. Some hours after moistening the dry filaments, the regular 
peripheral disposition of the fat-globules more or less disappears. 
With the advent of a dry period the protoplasts round oft' slightly and 
develop a new layer of membrane. The products of division of successive 
akinetes (i. e. the growth during the intervals between two periods of 
