A HISTORY OF HERTFORDSHIRE 



They are entirely aquatic, and have been termed by their chief 

 British investigators, Messrs. H. and J. Groves, 'the pioneers of aquatic 

 vegetation,' for they play the same part in the water as mosses do on the 

 land. They may generally be found in stagnant water, lakes, and slow 

 streams. The term 'stonewort' had been given to them on account of 

 the amount of lime which some species secrete. 



Of the thirteen British species of Chara, three of To/ype/fa, and seven 

 of Nitella, the following are present in Hertfordshire 1 



Chara fragilis, Desv. 



vulgaris, L. ( = C. foetida, Braun) 

 Tolypella glomerata, Chev. 



intricata, Leonh. 



Nitella translucens, Ag. 



flexilis, Ag. 



opaca, Ag. 



Fruits or seeds of Chara, probably of existing species, have been 

 found in the ancient Hitchin lake-bed, but the genus existed in Britain 

 long before the Pleistocene period, occurring in Jurassic times in beds of 

 Wealden age. 



THE 



The Alga? are a very diverse class of plants, including such groups 

 as the seaweeds, confervas, desmids, and diatoms. All are aquatic or 

 hygrophilous, for some live on wet rocks or damp walls ; but very few 

 of these are recorded for the county, nearly all our known species fre- 

 quenting ponds and slow streams. The only rivers in which they have 

 here been found are the Lea and the New River, all our other streams 

 apparently being too rapid for them. 



Our knowledge of the Algas of Hertfordshire, exclusive of the 

 Diatomaceae, is almost entirely derived from Hassall's British Freshwater 

 Algce (1845), with a few records from the 'Transactions of the Hertford- 

 shire Natural History Society. Hassall records 120 'species' as occurring 

 in the county, nearly all being from the neighbourhood of Cheshunt, 

 with a few from Hertford Heath and one from Royston, but many of 

 his species are only varieties or forms of others, and a few cannot now 

 be identified. Excluding these, the number recorded by Hassall is re- 

 duced to eighty-six, and the total number now known is ninety-six, 

 as in the following table 



CoCCOPHYCE.ffi 



Pleurococcus 

 Porphrydium . 

 Scenedesmus 

 Pediastrum . 

 Chlamidococcus 

 Volvox . . . 

 Hyalotheca . 



DESMIDIEJE 

 Desmidium . 



Mesocarpus . . 7 

 Staurospermum . 4 



SIPHOPHYCE.S: 

 Vaucheria . . 7 



NEMATOPHYCE^ 

 CEdogonium . 1 6 

 Bulbochcete . . I 

 Hormiscia . . I 

 Stigeoclonium . 4 

 Draparnaldia . 3 



CYSTIPHOR.S: 



Chroococcus . i 



NEMATOGEN^ 



Oscillatoria . . 3 



Lyngbya. . . i 



Rivularia . . i 



Gloiotrichia . . i 



RHODOPHYCE^: 



Batrachospermum 2 



1 From the list, with- localities, of the Characeae of the South Midlands, given by Mr. James 

 Saunders in Trans, Herts Nat. Hist. Soc. vol. ix. p. 25 (1896). 



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