66 Microscopical Sorirfy. 



instrument, is the prevention of those accidental vibrations which so 



much interfere with microscopic 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 the instrument of 

 Mr. Jackson this principle lias been carried further than has hitherto 

 been effected ; and it also affords improved facilities for minute ad- 

 justments, and the accurate admeasurement of microscopic objects. 



A discussion ensued on the subject of Mr. Jackson's paper, and 

 also on the best methods of measuring microscopic objects, and the 

 greater difficulties encountered in ascertaining the antero-posterior 

 diameters of minute bodies, as compared with the facilities which 

 we possess of obtaining lateral measurements. The meeting then 

 resolved itself into a conversazione, during which a number of inter- 

 esting objects were exhibited by individual members, many of 

 whom had their microscopes upon the table. 



The meeting adjourned at 11 o'clock. 



Wednesday, February 19, 1840, R. H. Solly, Esq. in the Chair. 



A paper was read by Mr. Quekett, on the development of the 

 vascular tissue of plants, in which it was shown that the membra-, 

 nous tube of vessels originated from a cytoblast in a manner similar 

 to that described by Schleiden in the formation of cells*, from which 

 at first it is difficult to recognise them ; but in a short time they 

 assume a very elongated form, and the cytoblast disappears. Before 

 the fibre is deposited, the contents, which are gelatinous, are 

 crowded with numerous most minute granules, which possess the 

 motion known as " active molecules," and after a short time when 

 they have become a little enlarged, they adhere to the inner surface 

 of the tube containing them in a different manner for each vessel, so 

 that the several varieties of vascular tissue are not degenerations of 

 each other, but are each constructed originally on the plan they are 

 always observed to present to the eye. 



It had been conjectured by Schleiden that a current existed be- 

 tween the gelatinous contents of the cell and its walls, which pre- 

 ceded the formation of a fibre and gave the direction it afterwards 

 took ; this was refuted by showing that the granules become sepa- 

 rately attached to the inside of the vessel, a little distance from each 

 other, beginning first at one end and proceeding to the opposite ; 

 the fibre elongating like a root, by the materials of growth being 



* See Taylor's Scientific Memoirs, vol. ii. p. 281. 



