A HISTORY OF DURHAM 



the home of numerous species of Oscillarlece. Adhering to the sub- 

 merged stones, the gelatinous masses of Nostoc verrucosum are a noticeable 

 feature in some of the clear streams of the mountain limestone. 



Among the Green Algae (Ghlorophycece) the Desmids appear to 

 be specially abundant, finding a most congenial habitat in the peaty 

 pools so frequent among the moors. Here also species of Spirogyra, 

 Zygnema, and Mesocarpus are among the commonest forms to be observed. 

 In damp situations the barks of the trees are green with Pleurococcus 

 vulgaris ; Prasiola crispa is found by the roadsides, and the terrestrial 

 species of Vaucheria may be met with almost everywhere. The aquatic 

 genera Ulothrix, Coleocbteta, CEdogonium, Cbtztophora, Cladopbora, and 

 Vaucheria are abundant; Enteromorpba intestinalis occurs in ditches at 

 Hartlepool, and Palmella cruenta is very common in the Sunderland 

 district (Brady). Clathrocystis ceruginosa and Physactis parvula have been 

 noted from the moat at Raby (Norman) and Tetraspora lubrica at Ryhope 

 (Brady). The beautiful Draparnaldia plumosa is not uncommon, and 

 grows plentifully on the high ground between Allansford and the 

 Sneep. 



The Rhodophycecz, which make up such a large proportion of the 

 marine alga?, include only a few freshwater forms. In Durham the 

 two species of Batrachospermum, B. atrum and moniliforme, are common in 

 the streams of some of the hills and denes, and are also frequently met 

 with in the lower parts of the county. The green waving tufts of 

 Lemanea jluviatilis are found attached to the stones in the quieter parts 

 of the clear mountain streams, and Ghantransia chalybea clings closely to 

 the smooth surface of the rocks under the swiftly rushing water. 



Among the Characeee^ the species of Nitella and Chara are widely 

 distributed. Chara hispida grows in great profusion in the Hell Kettles 

 at Croft, and C. flexilis and C. fcetida also occur plentifully in the 

 county. 



MARINE ALG^E 



The bleak rugged coast of Durham, exposed to the full fury of the 

 wind, and swept by the cold waters of the northern sea, is not favourable 

 to a luxuriant growth of seaweeds. There is an absence of rocky pools, 

 and few sheltered bays. The temperature of the water varies consider- 

 ably between the east and west coasts. On the east coast the sea 

 temperature is much lower than on the other parts of the British Isles. 

 For example, in August it only rises to 1 5 C., while on the south and 

 west coasts 20 C. is attained. In February a marine isothermal of only 

 5 C. extends from the Naze to the Frith of Forth, the other parts of 

 the coast being 5 C. warmer. It is not surprising, therefore, that the 

 oceanic vegetation is greatly superior on the western shores, but one 

 would hardly expect to find Durham inferior in number of species to 

 Northumberland, which is further north, and possesses still fewer natural 

 advantages of situation. The Northumberland region, however, presents 

 thirty-three species not found in Durham, while the latter has only 



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