Desmarestia Dresnayi on the coast of Ireland. 293 



described and figured in the ' Dictionnaire des Sciences Natu- 

 relles/ t. xiii. p. 105, the figure being half the natural size. 

 Professor J. Agardh — the most recent authority — in his great 

 work, 'Species, Genera et Ordines Algarum,' refers both the 

 above Algae to varieties of Desmarestia ligulatOy but still includes 

 D. pinnatinervia among his " Species inquirendse,^' with the ad- 

 ditional remark, " videtur pars inferior frondis latioris Desma- 

 restise ligulatse/^ 



D. Dresnayi f Lam., which was published in 1819, was found 

 on the French coast. It has a slender stipes about half an 

 inch high, which immediately gives off two lateral fronds about 

 2 feet long and 1 to 2 inches broad, linear- lanceolate, with a 

 fine longitudinal nerve and very delicate opposite lateral nerves, 

 which are sometimes forked. The margin is sinuate, more or 

 less toothed, and towards the base some of the lateral nerves are 

 prolonged into very short leaves of the same form as the frond, 

 thus manifesting a tendency to the pinnate development charac- 

 teristic of the genus. The colour is described as olivaceous, and 

 the substance membranaceous. 



D. pinnatinervia, judging from the figure given by Dr. Mon- 

 tague, has so close a resemblance to D. Dresnayi, that were the 

 two side branches in the figure of the latter plant removed, the 

 remaining central portion (which appears to have been shortened 

 by some injury) would be almost a fac-simile of it. The cha- 

 racter of the nervation and of the margin is precisely the same 

 in both — so also is the stipes, the colour and the substance. The 

 frond, however, is quite simple, and Dr. Montague compares it 

 to large specimens of Laminaria debilis. 



With regard now to the Irish plants, they appear to constitute 

 an intermediate link between the two forms above mentioned. 

 They have a slender well-defined stipes half an inch long or 

 more, a linear- lanceolate frond from 12 to 18 inches long and 

 2 .to 4 inches broad, the margin more or less sinuate and den- 

 tate. An exceedingly fine but very perceptible nerve runs from 

 the base to the apex, from which, lateral ones opposite, and fre- 

 quently forked, are given off at intervals of nearly a quarter of 

 an inch. These lateral veins, which are somewhat inconspicuous, 

 at least in the dried specimens, terminate in the marginal den 

 ticulations. Mr. Sawers observes, that the colour in the fresh 

 state is that of a Laminaria, while the substance is thinner. That 

 gentleman also describes the margin in one or two specimens as 

 slightly proliferous ; bringing the plant so very near to D. Dres- 

 nayi, that I do not see how the two can be separated ; and the 

 latter name having the priority must be retained, if they are to 

 be considered as distinct from D. ligulata. 



It must be confessed that the transition from the ordinary 



