The Peridiniece of Sutton Park, Warwickshire. 183 
boggy parts of the Park, among submerged Sphagnum, but nowhere 
in such abundance as in this one ditch. The ditch was easy of 
access, and I thought it would afford an excellent opportunity for 
acquiring some information concerning the formation of resting- 
cysts in this species. Indiscriminate observations in various parts 
of the British Islands had led me to believe that the formation of 
cysts in Glenodinium uliginosum took place at almost any period of 
the year, and how far this belief was wrong will be seen from the 
following observations. 
Periodic collections have been made continuously for over two 
years from precisely the same spot in this boggy ditch, a spot easily 
marked owing to, the proximity of some wooden railings. These 
collections were commenced in October, 1906, in which month the 
Glenodinium was fairly abundant. Throughout November and 
December there was a falling off in numbers accompanied by the 
formation of numerous cysts. Cyst-formation commenced early in 
November, and by the third week in December the organism had 
completely encysted. From January (1907) to March, the number 
of motile individuals gradually increased, reaching a maximum 
towards the end of the latter month. From the end of March, 
through April, to the middle of May, there was a reduction in 
numbers, but from this period there was again a rapid rise to a 
great maximum in June. In July there was a second minimum, 
followed again by a third maximum in August. From the middle 
of August there was a gradual decrease in numbers until by the 
middle of December the organism had once more completely 
encysted. The observations were continued through 1908, and 
show a very similar sequence of three maxima and three minima in 
the yearly cycle of the organism. 
The first maximum is in March, the second in May or June, 
and the third is during August and the beginning of September. 
The first minimum occurs in April or May, and the second in July. 
Only partial encystment occurs, however, and motile individuals 
can always be found during these first and second minima. The 
third minimum occurred in the December of three consecutive years, 
complete encystment taking place, so that for a short period no 
motile individuals could be found. 
The relative abundance of the organism at different seasons of 
the year has been plotted out on the accompanying chart (Fig. 21), 
along with a curve of water-temperatures. The temperature of the 
submerged Sphagnum among which the Glenodinium occurred, was 
