BOTANY 



rush (Butomus umbellatus], and the water violet (Hottonia fa/usfris). 

 The last occurs also near Durham and Sunderland, and finds here its 

 most northern limit. The Hell Kettles, a remarkable series of large 

 deep ponds surrounded by boggy ground and overgrown with rushes and 

 sedges, is a botanical region worthy of note. Here grows the sedge 

 (CladiumMariscus), so valuable in the eastern counties for thatching; and, 

 among other rarities, Juncus obtusifolia, Carex stricta, the bladderwort 

 (Utricularia vu/garis), the mealy guelder-rose (Viburnum lantana), and 

 the rough stonewort (Cbara bispida), all denote the peculiar features of 

 a fen vegetation. Iris fcetidissima is a very rare plant found in the damp 

 woods. The flora of the magnesian limestone district is in great 

 contrast to that of the boulder clay and the coal-measures. The warmer, 

 better-drained soil supports again the lime-loving plants, and the special 

 limestone species of the west are thus once more freely met with in 

 the east, with the addition of some nine species which are confined to 

 the magnesian formation. These are the perennial flax (Linum perenne), 

 the bearded St. John's wort (Hypericum monfanum), the sainfoin (Ono- 

 brycbis satrva), the woolly-headed thistle (Carduus eriophorus), the privet 

 (Ligustrum vu/gare), the dwarf orchis (Orchis usfu/afa), the bee orchis 

 (Opbrys apifera)) the fly orchis (0. muscifera), and the upright brome- 

 grass (Bromus erectus). The low hills to the east are intersected by 

 picturesque denes and ravines, in the upper part often so confined as to 

 be impassable, and gradually widening as they approach the shore. A 

 rich flora of shade-loving plants clothes the sides and floors of these denes, 

 and many rare species luxuriate under the protection of the sylvan 

 vegetation. Castle Eden Dene, the most considerable and beautiful of 

 them all, is especially noteworthy as sheltering a much prized orchid 

 peculiar to the limestone, the lady's slipper (Cypripedium Calceolus]^ 

 which was once plentifully distributed there, but now requires very 

 careful preservation to save it from extirpation. Some of the rare 

 orchids mentioned above, as well as the narrow-leaved helleborine 

 (Cephalantbera ensifolia), are found in the deep recesses of this and other 

 denes of the magnesian limestone. 



The coast line of Durham, some forty-five miles in length, lies wholly 

 between the mouths of the rivers Tyne and Tees. Steep grassy slopes 

 alternate with magnesian limestone cliffs, which at Marsden and north 

 of Hartlepool stand out in bold rugged outline; desolate sand dunes 

 stretch along the shore towards the Tees mouth, and are succeeded by 

 salt marshes near Middlesbrough. A long coast line of such varied 

 character is peculiarly favourable for maritime vegetation, and the 

 different physical formations support each their special plant-associations. 

 South of the Tyne lies an open stretch of sand bordered by grass-covered 

 slopes ; here in former days were deposited large heaps of ballast from 

 the vessels entering the Tyne. Similar ballast heaps are to be found at 

 Sunderland and Hartlepool. Baker's list includes more than 150 species 

 of plants which have been thus introduced, but he states that it rarely 

 happens that any of these ballast introductions ripen seed and spring up 



43 



