380 Royal Society. 



perfectly healthy and filled with sap. On each of the following days 

 additional portions of the stem became affected in succession ; but 

 the unaffected parts still preserved their healthy appearance, and 

 the flowers and leaves developed themselves as if the plant had ve- 

 getated in pure water and the whole stem had been in its natural 

 healthy state. On a minute examination it was found that calomel, 

 in the form of a white substance, had been deposited on the internal 

 surface of the cuticle ; but no bichloride of mercury could be de- 

 tected in those parts which had retained their vitality ; thus showing 

 that the solution of the bichloride had been decomposed into chlo- 

 rine, calomel, and water, and had destroyed the vitality of the parts 

 where this action had taken place ; after which, fresh portions of the 

 solution had passed through the substance of the poisoned parts, as 

 if they had been inorganic canals. Various experiments of a similar 

 kind were made on other plants, and the same conclusions were de- 

 duced from them. 



As the addition of a solution of iodide of potassium converts the 

 bichloride of mercury into an insoluble biniodide, the author was 

 enabled, by the application of this test to thin sections of the stems 

 of plants into which the bichloride had been received by absorption, 

 to ascertain, with the aid of the microscope, the particular portion 

 of the structure into which the latter had penetrated. The result 

 of his observations was, that the biniodide is found only in the in- 

 tercellular and intervascular spaces, none appearing to be contained 

 within the cavities of either cells or vessels. 



As the fluids contained in the vessels and in the cells hold in so- 

 lution various vegetable compounds, their density is greater than 

 the ascending sap, which is external to them, and from which they 

 are separated by an intervening organized membrane. Such being 

 the conditions requisite for the operation of the principle of endos- 

 mose, the author infers that such a principle is constantly in action 

 in living plants ; and that it is the cause of the continual trans- 

 mission of fluids from the intervascular and intercellular spaces 

 into the interior of the vessels and cells, and also of the ascent of 

 the sap. 



Jan. 19, 1843 — " On the minute structure of the Skeletons or hard 

 parts of Invertebrata," by W. B. Carpenter, M.D. 



The present memoir is the first of a series which the author 

 intends to communicate to the Society, and relates only to the Mol- 

 lusca ; and he proposes, hereafter, to extend his inquiries to the 

 skeletons of the Echinodermata, and the various classes of articu- 

 lated animals. After adverting to the classifications of shells pro- 

 posed by Mr. Hatchett and Mr. Gray, from the propriety of which 

 he finds reason to dissent, he proceeds to state the results of his 

 microscopic examination of the texture of shells under the several 

 following heads. First, shells having a prismatic cellular structure, 

 as the Pinna, and which are composed of a multitude of flattened 

 hexagonal calcareous prisms, originally deposited in continuous 

 layers of hexagonal cells, and thus constituting a calcified epithe- 

 lium, analogous with the enamel of the teeth. Secondly, those con- 



