A SYSTEMATIC AND STRUCTURAL ACCOUNT OF AVRAINVILLEA. 67 



The land-form is very robust, and differs in some degree from 

 that of any of its congeners. With a general resemblance to that 

 of P. varians, it has very thick coriaceous leaves, which vary in 

 shape from broadly ligulate to elliptical ovate or orbicular. The 

 rosettes of clustered leaves are sometimes formed at the end of a 

 short erect stem, as in P. Zizii, and these stems occasionally 

 produce lateral branches. When forsaken by the water, the 

 already-formed stems continue to produce fresh leaves, which are 

 coriaceous, and enable the plant to grow so freely that I have seen 

 it in flower on the mud of a perfectly dry ditch. It seems as much 

 at home under such circumstances as Utricularia vidr/aris, which 

 flowers freely out of water, and assumes the appearance of a land plant. 



At present I can give only a single locality for P. falcatus, near 

 Kamsey, in Huntingdonshire, where its distribution over one or two 

 miles of fenland suggests that it was formerly an inhabitant of the 

 boggy margins of the chain of meres which connected Whittlesea 

 Mere with the old River Nene. But I think it hkely that some 

 other remarkable Huntingdonshire forms are varieties of this 

 species, and I have seen plants from other British and Irish 

 localities which probably belong to it.* 



Explanation of Plates. 



Plate 286. — Potamogeton falcatus. 1, Upper part of flowering stem ; 2, sub- 

 merged nitens-like leaves ; 3, lanci-form with tuberous stolon ; 4, fruit-spike ; 

 5, drupelet, nat. size and mag. N.B. — The submerged leaves have only three 

 lateral ribs on each side of the midrib. 



Plate 287 .—Potamogeton varians Morong ined. 1, Upper part of flowering 

 stem with ripe fruit- spike ; 2, autumnal barren shoot ; 3, tuberous rootstock ; 

 ■4, land-form ; 5, drupelet, nat. size and mag. 



A SYSTEMATIC AND STRUCTURAL ACCOUNT OF 

 THE GENUS AVRAINVILLEA Decne. 



By George Murray, F.L.S., and Leonard A. Boodle, F.L.S. 



I. — Systematic. 



The genus Avrainvillea was founded by Decaisne, in 1842, in 



his 'Memoire sur les Corallines' (Ann. Sci. Nat. Ser. 2, Tom. xviii.), 



on an Alga found by d'Avrainville at the lies des Saintes, near 



Guadeloupe. The only species described was A. nigricans Decne. 



* Since the above note was written, T have had a further communication 

 from Mr. Beeby, which, in justice to him, I append, and Avhich strongly 

 supports my views on the hybridity of P. nitens : — "With regard to your 

 P. falcatus, I should not now place it under nitens; after examining quantities 

 of the latter plant in Surrey last year, in various stages of growth, and several 

 gatherings in Shetland, I have found it to be absolutely sterile — a point in 

 favour of the view held by some botanists, that it is a hybrid, I should accord- 

 ingly be disposed to keep your plant distinct ' (W. H. Beeby, in litt., Feb. 15, 

 I8b9). I should be thankful to any botanist who would send me specimens of 

 P. nitens — or supjwsed nitens — in fruit, and would gla'Uy send in return examples 

 of the fenland critical forms, such as P. coriaceus, P. varians, and P. falcatus. 

 My address is — Alfred Fryer, Chatteris, Cambridgeshire. 



F 2 



