194 G. S. West and Clara B. Starkey. 
A CONTRIBUTION TO THE CYTOLOGY AND 
LIFE-HISTORY OF ZYGNEMA ERICETORUM (KUTZ.) 
HANSG., WITH SOME REMARKS ON THE 
“GENUS” ZYGOGONIUM. 
By G. S. West, M.A., D.Sc., F.L.S., 
and Clara B. Starkey, M.Sc. 
[With Five Figures in the Text]. 
LTHOUGH Zygnema ericetorum is a common alga with a 
world-wide distribution, we have known very little concern¬ 
ing its cytological structure and still less about its conjugation. 
During the past few years the authors have been investigating 
the cytology of various specimens from widely different localities, 
more especially with regard to the exact nature of the chloroplast. 
It has also been continuously studied in the field for a period of 
over fourteen months, and various cultural experiments have been 
conducted in the hope of inducing it to conjugate. 
It can be regarded as the most inert of all the species of 
Zygnema. Considering that it grows equally well on damp ground 
and in peaty water, a fact which is not true of any other member 
of the Zygnemaceae, and appears very rarely, if ever, to conjugate 
in these habitats, it may be regarded as an alga which responds 
very little to the external influences which are known to induce 
many changes in other green algae. 
Fresh material of both the terrestrial and aquatic forms was 
studied from various localities in the British Islands, and fixed 
material from other parts of the world was also examined. 1 
I. Cytological Structure. 
The cell-wall. Tests with chlor-zinc-iodine, iodine and 66 per cent, 
sulphuric acid, and also strong sulphuric acid prove that the wall 
consists of cellulose. When tested with strong caustic potash the 
wall swells greatly and may appear slightly lamellate. During this 
treatment the phycoporphyrin and the oil-drops pass out through 
the wall, while at the same time the chloroplast and the two 
pyrenoids become very distinct. Some filaments possess a more or 
less distinct gelatinous sheath, often wide, and with a somewhat 
irregular outline. This feature can be made very evident by the 
use of potassium chromate and lead acetate. 
' An account of this work was given by one of the authors before Section 
K at the meeting of the British Association in Birmingham in 1913. Vide Brit, 
Assoc. Report, 1913, p. 716. 
