COLLECTED IN THE SOUTH ORKNEYS. 351 
tubes. Tt appears that such groups of cells are not necessarily formed only 
in the marginal portion of the thallus. In some specimens there were 
extensive strips of the thallus in which the cells were obviously in a moribund 
condition, and in the centre of such patches there was often a small rounded 
group of living cells with very abundant contents, The surrounding dying 
cells were of considerably larger dimensions than the others and looked as 
though they had not divided recently, No doubt, the central group of living 
cells becomes freed by the dying away of the surrounding part of the thallus 
and acts as an organ of vegetative propagation. 
The cells of the South Orkneys material had а curious purplish or olive- 
brown tinge, which is probably due to the action of the preservative 
(Г, phenol) ; staining with iodine brought out the chloroplast and pyrenoid 
very plainly. The dimensions were as follows :—width of cells =4р; 
length =6 ш; thickness C. e. dimensions at right angles to surface of 
thallus) =13 м. "There was always only a single layer of cells. 
CONJUGATE. 
MESOTZENIACE.E. (sensu Oltmanns). 
30. MESOLENIUM Ex pLicuEmaNUM, Naeg. Gatt. einzell, Ma, 1849, p. 109, 
{ 6 B5 West § West, Brit. Desm. 1904, р. ob, pl. 4. Вох. 20, 21. 
Sample 15, fairly common ; samples 1 and 3 (yellow snow 1), isolated. 
There appeared to be more than two pyrenoids, Cells 24 26 u long. 
8-9 ш broad. 
9l. ÜYLINDROCYSTIS BRÉBISSONII, Menegh. Monogr, Nostoch. 1542, р. 
t. 12. Но. 15: West § West, Brit. Desm. 1904, р. 98, pl. 4. Виз, 23-32. 
Sample 8, fairly common. Previously recorded from South Georgia 
(Reinsch). 
Two elongated pyrenoids mostly very obvious. Length of cells 2250-24 ш; 
breadth = 13 м. 
fig. C, 1-2; West у West, Brit. Desin. 1904, p. 99, pl. 4. figs, 33-38, 
Samples 8 and 9, fairly common. 
Cells 32-35 м long ; 14-15 broad. Two rounded pyrenoids. Cells 
occasionally very slightly curved. with broadly rounded ends, 
ZYGNEMACE.E, 
33. MOUGEOTIA sp. 
"ample 8 : only one filament of four cells seen. 
Cells 31 м broad ; six times as long. 
