VOL. LIX.] PHILOSOPHICAL TRANSACTIONS. SQQ 



to Qpnceive, that a paper of so delicate and uniform a texture as that of Cortona 

 should owe its origin to so complicated and remote a cause. 



To bring the matter in question to a more certain issue, Mr. S. examined the 

 threads of this paper with a good microscope ; and found them to consist of 

 mere filaments of the common species of conferva, without the intervention of 

 any other plant whatever. It was easy enough to ascertain the identity of the 

 conferva, the filaments of which it is composed being of a peculiar structure, 

 and very different from those of any terrestrial plant ; besides, as they are soli- 

 tary in their natural state, they undergo no other alteration by the above mecha- 

 nism, than the loss of the parenchyma that invests them, the structure of the 

 filaments themselves remaining as perfect as ever. 



To confess the truth, says Mr. S., I was but very superficially acquainted with 

 this species of conferva till I had made the above discovery ; since the descrip- 

 tions of it, which we find in the books of botany, by no means afford an ade- 

 quate idea of the structure of the plant. Dillenius, in his description of it, 

 pretending to correct Pliny, for a supposed impropriety in the term fistulosae 

 densitatis, says, that there is no cavity observable either in this or other larger 

 species of conferva, excepting, perhaps, in his conferva dichotoma ; in which he 

 is certainly mistaken ; since the filaments of the common conferva, when exa- 

 mined with a good microscope, evidently appear to be capillary tubes divided at 

 equal distances by parallel septa or diaphragms, exactly like the 25th species of 

 the same genus in Dillenius's Tables. Pliny's epithet, therefore, so far from 

 being improper, is a real characteristic of the thing in question. 



As the systematical botanists generally take their leading characters from the 

 external figures of plants, we need not be surprised to find them inaccurate in 

 their descriptions of the smaller tribes ; more especially as they neglect the use 

 of proper glasses, by which alone they can acquire a knowledge of them. Dil- 

 lenius and Linnaeus himself have both been led into mistakes, from this omis- 

 sion. The former, in the preface to his Historia Muscorum, confesses, that he 

 made use of common glasses only, in order that the figures of the smaller plants, 

 which he was to represent in his Tables, might not deviate too much from the 

 natural appearance of the plants themselves to the naked eye : and it is pretty 

 evident that the glasses he used were but of moderate powers, since, besides 

 other mistakes, they left him quite undetermined whether his 4th and 5th 

 species of conferva hat! ramifications or not, though this very distinction forms a 

 separate series in the first ordo. Linnaeus's generical character of this plant is 

 certainly less defective than that given by Dillenius, inasmuch as he takes notice 

 of the tubercula omitted by the former, and calls the fibres of the conferva capil- 

 lary ; but as he does not expressly say, whether these fibres are tubes or not, 

 and takes no notice of the septa or diaphragms distributed at equal distances 



