1913-14.] BOTANICAL SOCIETY OF EDINBURGH 281 



PlLULARIA GLOBULIFERA, LlNN., IN GLAMORGAN. 



By M. Y. Orr. (Plate XVII.) 



(Read 12th March 1914.) 



In the flora of Glamorgan, three separate localities are 

 given for Pihdaria globidifera, Linn., the earliest record 

 of its occurrence in the county dating from the beginning 

 of last century. Two of the stations mentioned are 

 mountain tarns, in one of which such plants as Lobelia 

 Dortmanna, Linn., and Isoetes lacustris, Linn., occur. In 

 these hill stations Pilularia is extinct, and, at the present 

 time, this plant is found in only one locality in the county, 

 a peaty moorland pool, situated near the hamlet of Welsh 

 St. Donats, about 400 feet above sea-level. 



In this pool Pihdaria is very abundant, and the 

 associated vegetation has much in common with that 

 usually met with in similar situations. On the other 

 hand, certain species which one might expect to find 

 represented there do not occur, although they are frequent 

 associates of Pihdaria in other countries, and under 

 apparently similar environmental conditions. A brief 

 description of the locality and its flora may therefore not 

 be out of place. 



The pool is roughly triangular in outline, and is about 

 300 yards long. It overlies a substratum of glacial sand 

 and gravel, and is surrounded by a tract of moorland, 

 which merges on all sides into agricultural land. This 

 sheet of water is fed by a short streamlet, which has its 

 source in swampy ground 100 yards distant. At the 

 lower end the outflow is controlled by a sluice-gate. The 

 area is subjected to an annual rainfall of over 40 inches, 

 and the level of the water-surface varies from time to 

 time. The climate is mild, and the freezing of the 

 water is a comparatively rare occurrence, and of short 

 duration. 



The water is distinctly peaty, gives an acid reaction, and 

 is poor in the constituents of plant food. A sample of the 

 water was found to contain the following amounts per 

 gallon: — 2127 grains of calcium carbonate, "837 grain of 



