199 
The Cytology of Zygnema ericetorum. 
of only a few cells with thick walls. The “ cysts ” remained in a 
state of inactivity until about the middle of March, when the cells 
showed signs of activity. A new thin cell-wall was formed within 
the old one, and the resumed growth caused many of the old cells 
to he broken through. In April growth and division of the cells 
had produced long filaments. The oil-globules were much reduced, 
so that the chloroplast and the two pyrenoids could be seen more 
distinctly. 
Similar “cysts” were formed in the aquatic form of the alga, 
and when examined immediately after the winter condition the 
resumption of activity was very plainly marked, the old thick walls 
of the cells being greatly separated by new growth with much 
thinner walls. 1 
Another terrestrial form from the west of Ireland was cultivated 
from November, 1911 to June, 1913, the culture thriving on damp 
peat. By inadvertence it was only examined from January to June, 
1913. Numerous aplanospores were formed in January and February, 
one spore being formed in each cell. A curious fact should be here 
recorded, viz., that in most cases the whole contents of the cell 
were not used up in the formation of the spore, a small part of the 
protoplast being excluded (Fig. 3, D and E). A few cysts were 
formed, but these were rather unusual. The walls of the spores 
increased greatly in thickness and the contents turned brown. At 
the latter end of February the spores germinated and by growth 
and division filaments of cells were quickly formed. 
A quantity of this terrestrial form from the west of Ireland 
was gradually raised to a temperature of 40°C. It was then allowed 
to cool slowly, and examined. Many of the cells had been killed; 
others had suffered no change; but in some the protoplast had 
rounded itself off and formed an entirely new cell-wall. 50’C. was 
fatal to all the cells of the filaments. 
2. The Influence of Moisture on the Terrestrial Form. 
In October, 1910, a number of filaments of the terrestrial form 
collected in Sutton Park, Warwickshire, were placed in a culture- 
vessel of rain-water. By November the cell-walls had increased in 
thickness and the filaments had become segmented into lengths of 
from 2 to 20 cells. Many of these short filaments of cells became 
rounded at the extremities and set free. In February, 1911, many 
cells in each filament were dead and the segments consisted of from 
1 This is a frequent condition in both terrestrial and aquatic species of 
Ulotlirix during February and March. 
