198 G. S. West and Clara B. Starkey. 
were coloured a deep brownish-red by alcannin solution, were 
blackened by osmic acid, and entirely removed by ether and absolute 
alcohol. The oil-globules begin to disappear normally in the late 
spring. Their presence renders the pyrenoids difficult of detection 
in unstained examples. 
II. Experimental Work. 
This work was primarily conducted in the hope of inducing the 
alga to conjugate and thus obtaining a possible clue to the physio¬ 
logical conditions essential for its conjugation. All the experiments 
were failures from this point of view, no conjugation having been 
observed in a single instance. 1 
1. The Influence of Temperature. 
These observations were carried out in one of the natural 
habitats of the alga in Sutton Park, Warwickshire, from October, 
1910 to April, 1911. The place selected was where the alga was 
growing on damp ground and fortnightly observations were made. 
In October, during comparatively mild weather, the filaments 
were of great length and the chloroplast was completely masked by 
large oil-globules. At this period the cell-wall had attained a 
considerable thickness. By the middle of November, colder weather 
having set in, some of the cells died, causing the filament to become 
segmented into short lengths of from 2 to 30 cells. The terminal 
cells of each length were rounded, but did not completely separate, 
being held together by the walls of the dead cells. At this period 
the oil-globules were much reduced in size. In January, in which 
month the ground became frozen, many more of the cells died, the 
filaments becoming segmented into shorter lengths of cells. All 
the cells contained numerous oil-globules. In February still more 
cells succumbed and the segmentation of the filament became more 
marked, each segment consisting generally of about four cells, 
occasionally of 10 or 20, and sometimes of two or only one. In 
many cases the filaments became dissociated into the separate short 
segments, which are of the nature of resting “cysts,” 2 consisting 
1 On one occasion, in a culture of the terrestrial form in rain-water, 
conjugation-tubes were put out from two cells in filaments lying side by side, 
The ends of these tubes had already started to fuse when conjugation was 
interrupted by the death of both protoplasts. This was the only instance 
observed of even an attempt at conjugation. 
In the course of the experimental work filaments from different parts of 
the British Islands were frequently mixed and allowed to grow side by side, 
but no conjugation took place. 
* For previous mention of these “ cysts ” in the Zygnemaceae and other 
Green Algae consult G. S. West, Treatise on British Freshwater Alga:, 1904 ; 
and in Journ. Linn. Soc. Bot., XXXIX, 1909, p. 34. 
