A HISTORY OF HERTFORDSHIRE 



with difficulty and yielding but a small detritus. The result would be 

 that hygrophiles or moisture-loving plants would be supplanted in the 

 struggle for existence by xerophiles or heat-loving plants which thrive 

 with a smaller amount of moisture. That is the principal change which 

 has taken place in our flora since the epoch of the Hitchin lake-bed 

 which immediately preceded the arrival of man in that district, and this 

 change is still going on, every bit of land which is drained and brought 

 under cultivation, and every drop of water abstracted from our under- 

 ground Chalk reservoir in excess of that which percolates into it, 

 hastening it on. 



We have now scarcely any purely eugeogenous soils. Of the 

 eighteen botanical provinces into which Hewett Cottrell Watson, in his 

 Cybele Brifannica, divided Britain, Hertfordshire is in two, the Thames 

 and the Ouse, and each of these provinces comprises two geognostic types, 

 dysgeogenous and subeugeogenous. Much the greater part of the county 

 is in province 3, Thames; only a small portion in the north being in 

 province 4, Ouse. In the Thames province it is only a small portion of 

 the county, the London Clay area in the south, which is subeugeogenous ; 

 and in the Ouse province the very small area of the Gault Clay in the 

 extreme west which is subeugeogenous may be disregarded for any 

 practical purpose. Very much the greater portion of the county, in both 

 the Thames and the Ouse provinces, therefore partakes of the dysgeogenous 

 type of each of those provinces. 



A list of 89 ' dysgeogenous species ' (xerophiles) of British flowering 

 plants and of 138 'eugeogenous species ' (hygrophiles) has been given by 

 John Gilbert Baker in a paper read before the British Association in 

 1855.* Of these we have in Hertfordshire 30 xerophiles, being about 

 33 per cent, of those enumerated by Mr. Baker, and only 10 hygrophiles, 

 or about 7 per cent, of the species which he enumerates. But this is 

 not all : our 30 xerophiles are comparatively common their relative 

 frequency in our six botanical districts may be expressed by the number 

 104 ; on the other hand our to hygrophiles are comparatively rare 

 their relative frequency in our botanical districts being represented by 

 the number 17. What is meant by this will be seen from the following 

 tables, which give the occurrence of each species in each of the six 

 botanical districts to be described presently. These lists might easily be 

 extended, but it is thought better only to include those species which are 

 enumerated by Mr. Baker. 



In these and all other tables of flowering plants the sequence of 

 species is the same as in Sir J. D. Hooker's Students F/ora, and the names 

 adopted by him are used. In some cases the names used in Pryor's 

 Flora are added as synonyms. 



1 ' The Flowering Plants and Ferns of Great Britain : an attempt to classify them according to 

 their geognostic relations' (1855). This paper, which was printed as a separate pamphlet, is mainly 

 based upon J. Thurmann's Essai de phytostatiyue . . . Jura . . . (Berne, 1849). 



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