EXHIBITION MEETING, 1952 
63 
l’<LA I’A LUSTliJS IN THE IhuTisH Isi.es 
'I’he exhibit routaiiicil a sketcli oi. the liistoi'y ut the discovery of 
/'. jidl iistria L. in Britain, and the d ifiVrini^ \ie\vs on its status; also 
a distribution map, notes on its liabitat at Wood Walton Fen, Hunts, 
and specimens, including one from this recently-discovered Hunts 
locality and from Wicken Fen, Candis. 
A lull account is being prepared for M’dt.simia. 
M. F. D. PooKE & S. M. Waeters. 
ALISMA rLANTACW-AQUATWA and A. LANCEOLATUM in the 
Cambridge District 
J. 1). Hooker in the Student’s Fiord of 1884 described only one of 
the present British species of Alisnia, A. lanveolatum being mentioned 
only as a \ariety of A. pkintago {-aquaticu). In the new Flora of the 
Jiritish Isles wc now find two separate species — A. pknitaqo-aquatica L. 
and A. la-nceulatuin With. Observations were made to determine the 
strength of this classification. 
The observations lead to the belief that A. plantuyo-aquatica and 
A. lunceolatum are indeed distinct species. Also, that hybrids and 
intermediates between them are not found in nature. This is in ac- 
cordance with: — 
(i) the difference in time of flowering. 
(ii) the genetic constitution. 
It is supported by evidence from : 
(i) habitat differences. 
(ii) floral morphology. 
(iii) leaf shape and dimensions — of which the latter is the moie 
easily demonstrated. In this case, use was made of the formula 
of allometric growth. 
Chromosome studies confirmed that A. plantdqo-dqudtioa was diploid 
(2n=:=14) and that A. laneeoUitum was tetraploid (2n = 28). The latter 
shows none of the characters associated with a newly formed autotetra- 
l>loid. The similarity in the distribution of the two species suggests 
that they have been distinct for a considerable time. 
C. A. Priestley. 
Photographs of some Rare or Locat. British Plants 
19 species were illustrated by photographs taken in situ, mainly 
during the summers of 1951 and 1952. The species illustrated were: — 
Draha aizoides L., Dknithus gratia nopolitanus Vill., Linum. anglieum 
Mill., Trifolium squamosum L., T. molin-erii Balb., Sedum rosea (L.) 
Scop., Asarum eurojmeum. L., Bartsi-a alpina L., Teucrium scordium L., 
Galium debile Desv., Girsium tuberosum (L.) All., Hammarbya paludosa 
(L.) Kuntze, Liparis loeselU var. ooata Riddelsd., Ophrys sphegodes 
