t 42 Fritsch . — Zlfe Morphology and Ecology of an Extreme 
the moderate rounding off of the protoplast, no changes seem to be con- 
nected with the production of these ‘ akinetes ’ (cf., however, below) ; the 
chloroplast or chloroplasts, as the case may be, are still recognizable and 
Fig. 2. Terrestrial form of Zygnema ericetorum from Hindhead. A, formation of akinetes and 
pigment-cells (the latter in black), b, impending rupture of a filament at a point where a pigment- 
cell is situated. C, obliteration of an empty pigment-cell by growth of adjacent akinetes. D, ordinary 
cells of the Hindhead form, showing the disposition of the fat-globules. E, cells of a filament that 
has been subjected to desiccation, showdng the dense peripheral layer of fat-globules, e', small part 
of one of these cells, in optical section, e", ditto, in surface view. F, cells of a dry filament, 
showing the large peripheral fat-masses that are sometimes found, g, filament, showdng divided 
akinetes and empty pigment-cells. H, diagram of a filament showdng the products of successive 
akinetes, I, II, in, IV. pigment-cell ; /., fat. (B and H, x 400 ; A, c, E, e", f, x 650 ; D and g, 
x 850 ; e' x 1200.) 
the purple-coloured sap appears unaltered. The response to drought is 
thus of a very simple kind. 
With a return of more favourable conditions, moisture is rapidly 
absorbed, as described above. The filament immediately resumes its 
normal appearance, and cell-division sets in sooner or later. If the akinete 
