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XXIV. On the early Stages of Development of Leraanea fluviatilis, Agardh. 

 By G. H. K. Thwaites, Esq., Lecturer on Botany and Vegetable Phy- 

 siology at the Bristol Medical School. Communicated by the Rev. M. J. 

 Berkeley, F.L.S. 



Read February 15th, 1848. 



J-T is not a little remarkable that the early condition of our very abundant 

 Lemanea fluviatilis should have so long escaped the observation of botanists, 

 and this can perhaps only be accounted for by the circumstance of its bearing 

 a very considerable resemblance to Trentepohlia pulchella, |3, chalybea, Harvey 

 {Conferva chalybea, Dillwyn), not only in its colour and general appearance 

 when growing, but also in the kind of situations in which it occurs ; the two 

 species, indeed, may not unfrequently be found growing intermingled. 



Towards the end of November the young Lemanea may be observed in the 

 greatest abundance in places where the species occurs, covering the surface of 

 stones with a uniform dark olive somewhat villous coating, and adhering with 

 such pertinacity by means of its minute roots, as not to be detached without 

 injury to these, or by removing a part of the stone on which it is growing. 



On examining more minutely the character of the plant in this early stage 

 of its growth, the structure will be found to consist of numerous conferva-like 

 filaments, of about one line in length, sparingly branched in the manner of 

 Trentepohlia or of Conferva glomerata. Each of its filaments is about xiW i"* 

 in diameter, and consists of a single row of cells, which are from four to six- 

 times longer than wide. The endochrome or colouring matter of the cells is 

 of a blue-green colour, and arranged in a spiral manner, except in the 

 terminal cells, where it is more abundant, and thus gives to these a darker 

 colour than the rest of the plant. In many of the cells, however, the spiral 

 vittee are so divided and contorted as to give the endochrome a reticulated 

 appearance. 



The structure, so far as has been now described, might well be mistaken 



VOL. XX. 3 G 



