156 VEGETATION OF THE PEAK DISTRICT [CH. 
related to the absence of a large number of lowland aquatic 
flowering plants. The shallowness of the streams assists 
towards the same result. The streams on the sandstones and 
shales are deficient in humous acids, except in the case of the 
streams which drain the peaty deposits of the plateaux. The 
streams of the limestones are not merely deficient in humous 
acids, but are actually alkaline in reaction. 
On the flatter moorland plateaux in streams draining from 
the peat moors, a pond weed (Potamogeton polygonifolius) is 
indigenous. This plant appears to be confined to acidic waters. 
A crowfoot (Ranunculus Lenormandt) is locally abundant in 
similar situations, as well as in small streams and swamps on 
the hill-slopes of the sandstones and shales. R. hederaceus is 
very much rarer. Glyceria fluitans and Callitriche stagnalis 
are found in the streams, in reservoirs and mill dams, and in 
swamps up to 1500 feet (457 m.). Montia fontana, M. minor, 
and Stellaria uliginosa are also locally. very abundant in the 
streams on the sandstones and shales. The Batrachian crow- 
foots are almost confined to the limestone streams, where, 
however, they are locally very abundant, especially so below 
500 feet (152 m.). Species of Chara are also limited to the 
calcareous streams, whilst Nitella opaca occurs rarely in both 
the calcareous and the non-calcareous waters of the district. 
Ostenfeld (loc. cit.) includes “the vegetation on cliffs over 
which water constantly trickles” with the vegetation of round 
springs and streamlets, and this appears quite a reasonable plan; 
and Ostenfeld (loc. cit.) is also quite reasonable in refusing to 
follow Jonsson in placing this type of vegetation with the moss- 
bogs described by Warming, which are characterized by stagnant 
and not by well aérated water. 
On the whole, however, flowering plants are not generally 
abundant in quickly flowing streams; but this deficiency is 
more than compensated by the great abundance and variety 
of liverworts and mosses. Bog-mosses (Sphagnum spp.) never 
occur in the streams of the limestone hill-slopes, and are not 
common in those of the siliceous hill-slopes except when these 
are rich in humous acids. Algae are locally abundant and 
equally characteristic, but have not been studied ecologically. 
The following liverworts and mosses have been observed in 
the streams of the southern Pennines: 
