1893.] tJie Flora of the Pollard Willows near Cambridge. 83 



C Trees along the Cam, left bank, from Chesterton to 

 Horningsea. A district fairly open, with a good many trees in it 

 and many hedges, passing near to gardens in several places. Ribes 

 consequently stands high. Elder, Kose and Hawthorn, hedge 

 plants, stand high, but trees scarcely appear in the list at all, none 

 being very near to the willows. 



D. Trees on the right bank of the Cam, from Ditton to 

 Baitsbite lock (i.e. opposite to about half of section C) and on 

 both banks from Clayhythe bridge to the lock at Bottisham. A 

 district of similar character to C, but being nearer to many ash 

 trees by the width of the river (30 metres) the records of ash are 

 very much more numerous. Nettles also are more plentiful, there 

 being many of them in fields near Ditton. 



E. Trees on the open meadow between Cambridge and Grant- 

 chester, and on Dernford Fen. A more open district than the 

 preceding, but with many hedges. Rose, Hawthorn and Elder 

 figure largely in the list, while nettles fall off. 



F. Trees along the left bank of the Cam, from Horningsea to 

 the top of the reach above Clayhythe (i.e. beginning of section B). 

 An open district, rather like the last. There being no gardens 

 near, Ribes falls very low, as also does Elder, there being very little 

 of it in the hedges. 



G. Trees on Lingay Fen, to the south of Cambridge. A 

 fairly open fen, but with hedges and trees within a short distance. 



H. Trees on various parts of Bottisham and Soham Fens. 

 These districts are really open fen, with the usual ditches in place 

 of hedges between the fields. Hedges, however, occur round the 

 farms, and these and the gardens account for the presence of Elder, 

 Ribes and Hawthorn. Rosa is conspicuous by its absence, and the 

 list consists almost entirely of herbaceous plants, the grasses 

 especially occurring in large numbers, forming half the list. 



The districts are thus arranged in a rough series, beginning 

 with those most thickly wooded and ending with the most open 



The results thus obtained present various points of interest, 

 which will now be discussed. 



The plants belong to 28 Natural Orders and include 61 genera. 

 Eleven genera of grasses occur, 6 each of Compositae and Rosaceae, 

 4 of Umbelliferae. 



If we take the actual number of records of each plant, and 

 leave out those forming less than one per cent, of the total, we 

 have left only 21 species (counting each of the four species of Poa). 

 Galium Aparine heads the list with no less than 16 "3 per cent., 

 and is closely followed by Sambucus and Rosa. Urtica and Cra- 

 taegus also form each more than 5 per cent, of the total. 



