126 Effects of Fresh Water on some Marine Productions. 



assisted by a good microscope, may open up still more satis- 

 factory views of the subject. 



With respect to the other two species, I can speak with less 

 precision ; I shall state, however, what I believe to have ascer- 

 tained, though I shall not venture to speak undoubtingly. 

 The C/lva dichotoma has a reticulated texture, which, as 

 Lightfoot observes, gives it the appearance, when magnified, 

 of belonging to the genus Flustra of corallines. Now it ap- 

 peared to me, when examining portions of this plant under the 

 influence of fresh water, and in the field of an Ellis's micro- 

 scope, that each of the cells which cause the reticulated appear- 

 ance was covered by a membranons lid, which, from the pre- 

 sence of the fresh water, burst up with violence. On examining 

 jFucus punctatus in the same way, soon after its first contact 

 with fresh water, I could perceive a very evident jerking mo- 

 tion occurring here and there over its surface, with an appear- 

 ance as if little facets or scales had been suddenly let loose, 

 like the lid of a hunting watch when the spring is pressed. I 

 must observe, however, that what I have stated of these last 

 two plants is to be considered as only an introductory view of 

 the subject, and that farther investigation will be necessary to 

 give absolute certainty. At the same time the analogy between 

 the phenomena presented by the three species mentioned is 

 so strong, that there can be little doubt of their being regulated 

 by the same law. I believe the C/^lva dichotoma gets paler by 

 immersion in fresh water ; but of this I am not prepared to 

 speak positively. Respecting the other two species there can 

 be no hesitation, they both give out their colouring matter 

 copiously to the fresh water in which they are placed, and that 

 in a very short time. If the Conferva setacea be spread on 

 paper in sea water, it retains its original hue ; there is no 

 bursting up of its septa, nor breaches in its sides, and it does 

 not tinge the paper on which it is spread. I have preserved a 

 number of specimens in this way. i^ucus punctatus, when 

 preserved in the same manner, retains its original deep hue, 

 and does not tinge the paper. The flaccidity which takes 

 place in them all is scarcely to be accounted for, except on the 

 principle that their texture is in some respect broken up, and 

 we may presume also that, as in Conferva setacea, both the 

 other species explode the contents of their cells or cavities. 



The circumstance of these plants giving out their colouring 

 matter to the paper on which they are spread has been often 

 remarked, but has never before, I apprehend, been suspected 

 of being connected with their vitality. That it is so, however, 

 the observations made above clearly demonstrate. For it is 

 not because the plant is dead that the colouring matter is given 



