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The Cytology of Zygnema ericetorum. 
forming new filaments. The material was still alive and in a fairly 
healthy condition in June, 1912. At this time a few of the cells 
had become greatly swollen and a new wall, quite spherical in shape, 
was formed within the old cell-wall. This was a case of aplanospore- 
formation, and the wall of the mother-cell broke across in order to 
allow the aplanospores to escape. 
Further experiments were made in allowing the alga to dry up. 
In October, 1910, some of the alga, along with the peaty soil on 
which it was growing, was put into a damp chamber. It grew very 
well vegetatively all through the winter. Some of the material was 
then allowed gradually to dry up from January to March. At the 
beginning of March the filaments were dismembered into short 
lengths of from 2 to 6 (occasionally 10 to 20) cells and the cell-walls 
had increased greatly in thickness. The majority of the dismembered 
portions consisted of very few cells and were of the nature of thick- 
walled “ cysts.” Each cell contained a small chloroplast from 
which the pyrenoids had disappeared, and oil-globules were either 
absent or of very small size. It was found that the more complete 
the drying the fewer the number of cells in the “ cysts.” When 
these cysts were subsequently supplied with moisture the cells 
soon began active division and long filaments were gradually formed. 
Some material of the terrestrial form from the west of Ireland 
was allowed to dry very gradually on its original substratum. This 
was from March to July, 1913. Many cells died, but both cysts 
and aplanospores were formed in abundance. 1 
3. The Effect of Nutrient Media. 
a. Filaments of the aquatic form were placed in a 02 percent. 
Knop’s solution in October. In November the chloroplasts were 
of a deeper green colour and the cells were dividing rapidly. At 
the end of February the filaments were of great length and were of 
a deep green colour. The chloroplasts contained two large pyrenoids, 
but were mostly hidden by numerous oil-drops which filled almost 
the entire cell. At the end of March the filaments were very long, 
quite healthy, and the cells were actively dividing. Some of the 
chloroplasts possessed three or even four pyrenoids. Occasionally 
one cell in each filament died, and at that point the filament became 
disjointed into two pieces. 
1 As an instance of the tenacity of life of this alga it may be here mentioned 
that the dried material was placed in the dark from the end of July until the 
end of November. When examined on November 29th there were plenty of 
short cysts and free aplanospores. In the former the chloroplasts of the cells 
were quite normal, containing pyrenoids and also, in many cases, oil-globules. 
