BOTANY 



fontana, Prunus spinosa, Poterium officinale, Pyrus torminalis (?), Hippuris 

 "vulgaris, Myriophyllum, Cornus sanguinea, Sambucus nigra, Eupatorium 

 cannabinum, Fraxinus excelsior, Menyantbes trifoliata, Lycopus europeeus, 

 Ajuga reptans, Alnus glutinosa, Quercus robur, Ceratopbyllum demersum, 

 Sparganium, Potamogeton crispus (and two other species of the genus), 

 Naias marina, Scirpus lacustris (and one other species), Carex. Several 

 species of Chara also occur. 



Mr. Reid remarks : ' Such trees as the oak, ash, sloe, cornel, elder, 

 and alder point unmistakably to a temperate climate, and the fauna and 

 flora as a whole suggest climatic conditions not differing greatly from 

 those we now enjoy. . . . The occurrence of Naias marina, now only 

 found in Britain in two of the Norfolk Broads, is singular, though the 

 plant was evidently more common in former times than it is at the 

 present day.' This is the only plant on the list which is not now found 

 in the county, and with this exception the whole of the plants are 

 common or fairly common with us ; more than half the number are of 

 the generally diffused or British type, two (Pyrus torminalis and Naias 

 marina) are exclusively English, one (Cornus sanguinea) is nearly so, and 

 the rest are mainly British but more frequent in England than in the 

 rest of the British Isles. By ' exclusively English ' is meant confined to 

 England in Britain, for all are continental, and all but Naias marina, 

 which is a French and south German plant only, are widely diffused over 

 the continent. 



There is one point of great interest in this assemblage of plants, 

 corroborating other evidence of the change which has taken place in our 

 climate. All the herbaceous species are hygrophilous or moisture- 

 loving, or actually water-plants, while one at least of the trees, the alder 

 (Alnus glutinosa} , grows only in wet places (on river-banks or in marshes). 

 Here we have an indication of very different conditions from those 

 which now prevail in the neighbourhood of Hitchin ; the lake, the swamp, 

 and the moist woods of this bygone period having given place to the dry 

 gravelly hills and open chalk downs which are so characteristic of the 

 north of Hertfordshire. 



While climate has by far the greatest influence upon the distribu- 

 tion of plants, that exercised by geological formations is next in import- 

 ance, and it should not be overlooked that geological formations have an 

 influence upon climate. On a damp soil, especially in a well-wooded 

 district, more rain will fall than on a dry soil, which will naturally tend 

 to be a barren one. When the Reading Beds and London Clay extended 

 over the whole of Hertfordshire and perhaps the greater part of the 

 county was forest or swamp, the rainfall would be heavier and the 

 temperature would probably be lower than at a later time, when the 

 greater part of the clays and sands of these formations had been carried 

 away, exposing the chalk beneath them, and when beds of permeable 

 gravel were deposited upon both clay and chalk. The subsoil, originally 

 eugeogenous, that is abrading easily and yielding much detritus, would 

 give place to a subsoil of a dysgeogenous nature, that is disintegrating 



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