80 PROCEEDINGS OF SOCIETIES. 



tubercles were pretty freely distributed over both surfaces of the pinna, on the mar- 

 gins as well as on the flat surfaces ; those seen on the margins, being in profile, 

 showed a hemispherical outline, the greater part of which projected beyond the 

 margin. I have no doubt of these tubercles being the fruit, and that they are to be 

 regarded as conceptaclcs and superficial. I examined pinnae from two other speci- 

 mens of I), ligulata, which I had in my possession some years, and in both I no- 

 ticed traces of the same appearance of fruit, but not nearly so distinct as those on my 

 first specimen. In these last the capsules and spores appeared to have discharged 

 their endochrome, which is very probable, as this genus is very impatient of fresh 

 water, or even exposure to the air, decomposition commencing almost immediately 

 after they are removed from the sea. If the mode of fructification is to guide us in 

 the arrangement of the genera under orders, I conceive Desmarestia should be re- 

 moved from the order Sporochnacas to Dictyotacae, as the fructification I have ob- 

 served in D. ligulata is much more conformable to the latter order than to that of 

 the former. I have not as yet perceived any symptom of fruit either on D. acu- 

 leata or D. viridis, but the scattered single spores, so very abundant on Mr. Sawer's 

 late important addition to British botany, Desmarestia pinnatinervia, cannot but be 

 the fruit of that species. These spores have the same pink colour as those of D. 

 ligulata ; but, instead of being in capsules, they appear on every part of the frond, 

 like strings of beads or chains. I think it not improbable that young spring plants 

 of the two other species, aculeata and viridis, will reward careful examination by a 

 discovery of their fructification, and I would recommend search to be made among 

 the Byssoid fibres with which the young plants are clothed. 



I take this opportunity to exhibit some specimens of Desmarestia Pinnatinervia, 

 for which 1 am under obligation to Mr. William Sawers, of Londonderry, to whom 

 belongs the honour of adding it to the marine botany of our country. Mr. Sawers 

 sent specimens of his plant to the meeting of the British Association, at Hull, and to 

 most of our best algologists, some of whom pronounced it a mere variety of a Lami- 

 naria. At length specimens reached Dr. Montague, of the French Institute, who 

 recognised it as his D. Pinnitinervia, a description and figure of which he gave 

 in the u Annales des Sciences Naturelles," for 1842, vol. xviii. As there are 

 some differences between the appearances of the Spanish plant, as described by Dr. 

 Montague, and those found by Mr. Sawers, I will refer to a free translation which 

 I have made of the article in the " Annales." 



u Is it truly a Desmarestia ? That is a question not easily decided, in the 

 absence of any fructification. M. Aghardh is inclined to believe it is to that genus 

 we should refer it. This alga requires careful description, because it has a perfect 

 resemblance to Laminaria debilis, collected on the coast of Corsica by my friend 

 Mr. Solierol. The only differences which I have found, though essential diffe- 

 rences, and which separate our plant from those with which I have compared it 

 are — first, the presence of a well-defined stipe, about four or five millimetres 

 long — second, a midrib, which traverses the entire length of the frond, and from 

 which nervures issue to the right and left, at the distance of five and ten millimetres 

 from one another, forming, with the midrib, angles of about 24 degs. All these 

 nervures, though strongly marked, are of the greatest tenuity. The form of the 

 frond is obovate, fourteen millimetres long by eight in width at the widest part, 

 which is the summit. It has the same delicate tissue as Laminaria debilis. If it 

 is a Desmarestia, as all believe it to be, we must consider the frond as formed by 

 the fusion of the opposing pinnules, which will represent the nervures." 



The differences which I find between the Spanish plant as described by Dr. 

 Montague, and the specimens of the Irish plant supplied by Mr. Sawers are — The 

 Spanish plant is dentated at the margin, obovate, and the widest at the summit. 

 Mr. Sawer's specimens are entire at the margin, very slightly waved, lanceolate, 

 and widest about one-fourth of the length of the frond from the base, tapering 

 thence towards the summit; the proportions of length and breadth of the two plants, 

 are very dissimilar. However, I am inclined to regard them at present as iden- 

 tical, merely altered by the circumstance of climate. It is singular that, although 

 the figure given in the u Annales" exhibits an appearance of dots, Dr. Montague has 

 made no mention of chain-like series of spores, such as are contained in the dots in 

 Mr. Sawer's plants. 



