DITBLIIf K ATUBIL HI8T0RT SOCIETY. 35 



D. Ugulata, which I had in my possession some years ago, and in both I noticed 

 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 hare dis- 

 charged their endochrome, which is very probable, as this ^enns is very im- 

 patient of fresh water or even exposure to the air, decomposition commencing 

 almost immediately after they are removed from the sea. If the mode of fruc- 

 tification is to guide us in the arrangement of the genera into orders, I con- 

 ceive Desmarestia should be removed from the order Sporochnacese to Dictyo- 

 taceie, as the fructification I have observed in D. ligulata is much more 

 comformable to the latter order than to that of the former. I have not as yet 

 perceived any symptom of fruit either on D. aculeata, or D. viridis, but the 

 scattered single spores so very abundant on Mr. Sawers'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 pinnati- 

 nervia, for which I am under obligation to Mr. William Sawers of London- 

 derry, 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 aleologists, some of whom 

 pronounced it a mere variety of a Laminaria. At length specimens reached 

 Dr. Montague, of the French Institute, who recognised it as his D. pinna- 

 tinervia, a description and figure of which he gave in the '^Annales des Sciences 

 Naturelles" for 1842, vol. xviii. 



As there are some differences between the appearances of the Spanish plant, 

 as described by Dr. M., and those found by Mr. Sawers, I will refer to a free 

 translation which I have made of the article in the ^' Annales.** " Is it truly a 

 Desmarestia? That is a question not easily decided in the absence of any fruc- 

 tification. M. Agardh 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 M. Solierol. 

 The only differences which I have found, though essential differences, and which 

 separates our plant from those with which 1 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 to ten millimetres from one 

 another, forming with the midrib angles of about 24 degrees. 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 of 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 widest at the sum- 

 mit. Mr. Sawers' 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 the length and breadth 

 of the two plants are very dissimilar. However, I am inclined to regard them 

 at present as identical, merely altered by the circumstance of climate. It is 

 singular that, although the figure given in the Annates 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. Sawers' plants. I imagine, from these spores 

 on our Irish specimens, that the exotic ones have them also. By some it baa 

 been doubted if the plants taken at Lough Foyle are indigenous to that coast, but 



