152 SCIENTIFIC INTELLIGENCE. 



is tlie prevention of those accidental vibrations which so much interfere 

 with microscopical examinations, especially in the neighbourhood of 

 crowded thoroughfares. This object is effected by connecting together 

 the body and stage of the instrument, in such a manner that whatever 

 vibrations are communicated to the one shall be equally communicated 

 to the other. In Mr. Jackson's instrument this principle has been car- 

 ried farther than had hitherto been effected; and it also affords improved 

 facilities for minute adjustment, and the accurate admeasurement of 

 microscopic objects. 



The second meeting of this Society was held on Wednesday, the 

 19th of February; R. H. Solly, Esq., in the chair. 



A paper was read by Mr. Quekett, * On the development of the vas- 

 cular tissue of plants ; ' in which it was shown that the membranous 

 tube of vessels originated from a cytoblast, in a manner similar to that 

 described by Schleiden in the formation of cells. Before the fibre is 

 deposited, the contents, which are gelatinous, are crowded with numer- 

 ous most minute granules, which possess the motion known in " active 

 molecules: " and after a short time, when they have become a little en- 

 larged, they adhere to the inner surface of the tube containing them, in 

 a different manner for each vessel ; so that the several varieties of vas- 

 cular tissue are not degeneiations of any other kind, but are each con- 

 structed originally on the plan they are always observed to present to 

 the eyei. 



It had been conjectured by Schleiden that a current existed between 

 the gelatinous contents of the cell and its walls, which current preceded 

 the formation of a fibre, and gave the direction it afterwards took ; this 

 was refuted by showing that the granules become separately attached 

 to the inside of the vessel, a short distance from each other, beginning 

 first at one end and proceeding to the opposite one ; the fibre elongat- 

 ing like a root by the materials of growth being always added to the 

 point. The granules so attached become nourished by the contents of 

 the vessel, and the spaces between them are in a short time obliterated 

 by the fibre acquiring a defined border, which completes its development. 



This act is the one observed in the formation of all vessels ; but the 

 arrangement of the granules differs, so as to constitute the several va- 

 rieties. In the annular vessel the granules attach themselves horizon- 

 tally, forming rings ; — in the spiral they become inclined, and by 

 continuing this direction around the interior of the membranous tube 

 the peculiar character of this vessel is obtained : — in the reticulated^ 

 for each division or branch of the fibre, a gi'anule becomes enlarged in 

 the line, and fonns the starting-place for the fresh direction of the fibre. 

 In the dotted and scalariform vessels, the fibres become so reticulated 

 as to leave portions of the outer membrane of the vessel without any 

 deposit within; and this spot so left constitutes the dot or linear 

 marking seen on these vessels. 



This dot is plain in all such kinds of vessels, excepting those found 

 in woody exogens, where it possesses (from a slight difference of struc- 

 ture), a central mark analogous to that on the woody tissue of coni- 

 ferous plants, with which Mr. Quekett considered it identical, only of 

 a smaller size. 



