136 Fritsch . — The Morphology and Ecology of an Extreme 
A. The Cell-contents. 
The accounts as to the nature of the chloroplasts vary considerably. 
Schmitz (’ 83 , pp. 18, 44) describes them as closely resembling those of other 
species of Zygnetna . Wille (’ 90 , p. 20), in the first edition of Engler and 
Prantl’s ‘ Natiirliche Pflanzenfamilien speaks of two axile irregular chloro- 
plasts, occasionally coalescing (zusammenfliessend) to form an axile strand, 
whilst in the ‘ Nachtrage ’ (Wille, ’ 09 , p. 11 ; cf. also Borge, T 3 , p. 37) 
he corrects this to read ‘ one axile chromatophore with one pyrenoid ’. 
Lagerheim (' 95 , p. 15, foot-note 3) compares the chloroplast with that of 
Mougeotia , and a similar attitude is taken up by Bohlin (’ 01 , p. 51). In 
their recent paper, West and Starkey (T 5 ) come to the conclusion that in 
each cell of Zygnema ericetorum there is normally only one large axile 
chloroplast of indefinite outline. ‘ It is usually constricted in the middle 
and in some cases twisted. There are two large pyrenoids, one in each half 
of the chloroplast ’ ( 1 . c., p. 205). These conclusions are based on a study 
of carefully fixed and stained material from various localities. 
There can be no doubt that West and Starkey’s conclusions are true 
for the ordinary aquatic and terrestrial forms, but they are certainly not 
applicable to the terrestrial form found at Hindhead. The chloroplasts 
are, in this case, quite often well defined in the living cell, and can be made 
to stand out very clearly by treatment with a 8-10 per cent, solution of 
sodium chloride. In the shorter cells (Fig. 1, G; Fig. 2, D) but a single 
chloroplast is present, generally with only one pyrenoid. The chloroplasts 
are, however, quite unlike those figured by West and Starkey, being more 
or less star-shaped and similar to those of other species of the genus 
Zygnema . although rather more massive, so that the stellate character is less 
pronounced (Fig. 1). In the longer cells there are often two chloroplasts 
of this pattern, seemingly quite distinct and, if connected at all, the bridge 
between them must be exceedingly delicate (Fig. 1, A, b). In other cases 
these longer cells showed an obvious connexion between the chloroplasts, 
but it should be pointed out that the individuality of the two portions of 
the chloroplast was much more sharply marked than is shown in West and 
Starkey’s figures of the ordinary terrestrial form. 
Cell-division was only observed in cells containing either two chloro- 
plasts or a chloroplast that was already constricted into two very obvious 
portions. Each daughter-cell receives one of the two chloroplasts, so that 
for a time the young cell has but a single chromatophore (Fig. 1, b-d). 
Sooner or later the chloroplast and pyrenoid gradually broaden out axially 
(Fig. 3, d) and the pyrenoid divides into two (Fig. 1, E ; Fig, 3, E). At this 
stage, therefore, the cells contain an elongated axial chloroplast with two 
pyrenoids, more or less widely separated. Finally, the elongated chloro- 
plast becomes gradually constricted between the two pyrenoids (Fig. x, f) 
