44 Field Note. 



is clearly extra-areal in Lincolnshire, though no doubt areal in England 

 among rocks, such as we do not possess in this county. 



Mr. Clement Reid, F.R.S., also most kindly writes : — ' This plant — 

 Ballota nigra Linn, has always interested me, and I was a good deal sur- 

 prised when it turned up in the Cromer Forest Bed. However, at that 

 period the British climate was probably drier than now, though up till 

 now very few of the prairie plants have been found. 



' You may be interested to know that Ballota occurs not uncommonly 

 in Roman Silchester ; and I think also in Roman Caerwent, though the 

 specimen is too badly preserved for certainty. Silchester is on a gravel 

 soil over Bagshot Sands ; but there is a great deal of lime-rubbish about 

 the Roman town — cement, stucco, etc. 



' I cannot say that I feel very sure that Ballota may not be one of the 

 plants introduced in Roman times, for the only places where I found it 

 away from habitations and cultivated land are on old shelly beaches, and 

 by the shores of harbours, on steep banks. Still if the plant could live 

 under other conditions than those you give I think that 1800 years is 

 plenty of time for it to spread — the Linaria^ and Veronicas have no diffi- 

 culty in spreading. 



' In 1907 I found Ballota growing under exceptional conditions in Corn- 

 wall. There is a large field close to Wadebridge, attached to an old manor 

 house, and out of cultivation for many years. The whole of this field is 

 dotted with tufts of Cenfaurea scabiosa and Ballota mixed. This is so 

 iinusual that I tried to make out whether there was anything special 

 in the geology to account for it ; but it seemed to be merely rough 

 pasture on a thin soil overlying the ordinary non-calcareous slate of the 

 country. 



' However, there was formerly an enormous trade in shell sand for 

 manure between Padstow and Wadebridge, and possibly this field may 

 have been either heavily dressed, or have been one of the dumping places 

 for heaps of sand. The field, however, if I remember rightly, must be at 

 least two acres. It has sufficient slope to drain it well.' 



I do not suppose for one moment that Ballota, or any species of like 

 requirements, can have existed in Lincolnshire through glacial times. 

 I doubt whether such plants could even exist in Cornwall, but am in no 

 position to give an opinion. Mr. Clement Reid, in a letter says, ' It does 

 not seem probable that Ballota can have lived through the glacial period 

 in any part of the British Isles.' I believe the pre-glacial flora in Lincoln- 

 shire was wholly destroyed. The point is that what had once been could 

 exist again, if the climate were approximately the same. 



MOLLUSC A. 



Pisidium supinum Schmidt. (= P. conicum Bandon), 

 etc., in Lincolnshire. — Whilst searching for Pisidia at the 

 confluence of the river Brant with the Witham (div. 13 W.), on 

 July 24th, 1908, I took the above shell, making a new record 

 to the county list. Also on the 15th of the same month, at 

 Skirbeck, Boston (div. 12), Mr. Birchnall and myself obtained 

 some very characteristic forms of Planorbis spirorbis Miill. var. 

 leucostoma. Mr. J. W. Taylor has been kind enough to verify 

 the above specimens. — John F. Musham, Lincoln, December 

 23rd, 1908. 



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