284 TRANSACTIONS OF THE [Sess. lxxviii. 



Glamorgan station in many respects, but it also includes 

 Subularia, Lobelia, and Isoetes. 



Sturrock and Smith (1905) regard these plants as 

 distinctive of the " highland loch " vegetation, which is not 

 confined to high elevations, but is frequently met with 

 almost at sea-level. The lowland lakes of the Faroes, and 

 the moorland pools of Northern Germany, are characterised 

 by a similar aquatic vegetation, while in Southern Germany 

 its typical species ascend to an altitude of 2400 feet 

 (Issler, 1909). 



It is thus obvious that, under certain climatic conditions, 

 altitude is not the sole factor which determines the dis- 

 tribution of these " highland loch " types. Graebner (1901) 

 suo-o-ests that they owe their presence in these habitats to 

 the paucity of food material in the water, and this theory 

 is supported by Smith in his comparison of the vegetation 

 of highland and lowland lochs in Scotland. 



Should the climatic conditions be unfavourable, however, 

 altitude can no longer be regarded as a negligible factor, 

 as is shown by the distribution of these plants in 

 Glamorgan. Subularia does not occur in the county, but 

 Lobelia and Lsoetes, according to Trow (1911) and Riddels- 

 dell (1901), have long been established in two upland pools 

 at an altitude of 1500 feet, twenty miles distant from the 

 Pilularia station. They are absent from the pool at 

 Welsh St. Donats, although in its general features it closely 

 resembles the type of loch in which these plants occur. 

 The water is practically that of precipitation, while the 

 nature of the substratum presents no apparent obstacle to 

 the successful growth of the species referred to. 



It is therefore suggested that, in the milder climate, 

 the altitude factor does play a not altogether unimportant 

 part in the distribution of Lobelia and Lsoetes, while, in 

 their more northern stations, the climatic factor would 

 account for their occurrence at low levels. 



The introduction of these two plants into the pool at 

 Welsh St. Donats, on the lines of experimental ecology, 

 might be productive of some interesting results. 



