THE AUGUST HELEOPLANKTON ОЕ NORTH WORCESTERSHIRE, 423 
The August Heleoplankton of some North Worcestershire Pools. By 
В. Миллвр GRIFFITHS, M.Sc. (Communicated by Prof. G. S. West, 
М.А., D.Sc., F.L.S.) 
(PLATES 34 & 35.) 
[Read 2nd March, 1916. | 
Г. INTRODUCTION, 
Ту the rather hilly district of North Worcestershire a number of small 
streams are found. They are tributaries of the Stour or Severn, and run 
usually in valleys with fairly steep sides. The depth and narrowness of the 
valleys has made it an easy matter to construct dams, and consequently 
along the majority of the stream-courses series of artificial pools have been 
made. In past times the water-power was used to work various kinds of 
mills, including flour-mills, paper-mills, spinning-mills, and forges. At the 
present day many of these works are abandoned, and the pools are used 
chiefly for fishing. In many cases very considerable silting-up has taken 
place, and thick growths of reeds and water-weeds have been allowed to 
accumulate. 
During the years 1908-1910 a detailed investigation was made of the 
alga flora of Stanklin Pool, near Kidderminster *. It was thought advisable 
to examine other pools in the district, for the sake of comparison. In 
August 1910, collections of heleoplankton were taken from nine pools 
(including Stanklin) in the Kidderminster district. Seven of these are 
situated in the basin of the River Stour, and two in the valley of a small 
stream flowing directly into the River Severn. All these pools lie on the 
red sandstones of the Trias, and derive their water from those rocks, with 
the exception of pring Grove Lower Pool, which receives drainage from 
the Permian breccia and Old Red Sandstone of Trimpley. 
The plankton of the lakes of the British Isles f. has been investigated 
comparatively thoroughly during the last ten years; but little research 
has been undertaken on the plankton of smaller pools. It will be seen, 
however, from the results set forth in this paper, that small areas of water 
often possess alga floras of considerable interest. The pools examined show 
marked peculiarities in their respective floras. In many cases, also, species 
* b. Millard Griffiths, “ Algae of Stanklin Pool, Worcestershire," Proc. Birmingh. Nat. 
Hist. & Phil. Soc., 1912. 
t Consult summary of this in W. & G. S. West, * The British Freshwater Phytoplankton, 
with Special Reference to the Desmid-plankton and the Distribution of British Desmids,” 
Proc. Roy, Бос. B, vol. 81, 1909. 
LINN. JOURN.— BOTANY, VOL. XLIII. 2H 
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