ON THE VASCULAR TISSUE OF PLANTS. 69 



solution of potash ; by which process the air entered my mouth from 

 the flask through the caustic liquid, and the atmospheric air from with- 

 out entered the flask through the sulphuric acid. The air was of 

 course not at all altered in its composition by passing through the 

 sulphuric acid in the flask, but if sufficient time was allowed for the 

 passage, all the portions of living matter, or of matter capable of 

 becoming animated, were taken up by the sulphuric acid and destroyed. 

 From the 28th of May till the beginning of August, I continued un- 

 interruptedly the renewal of the air in the flask, without being able, 

 by the aid of the microscope, to perceive any living animal or vegetable 

 substance, although during the whole of the time I made my observa- 

 tions almost daily on the edge of the liquid ; and when at last I se- 

 parated the different parts of the apparatus, I could not find in the 

 whole liquid the slightest trace of infusoria, of confervse, or of mould. 

 But all the three presented themselves in great abundance a few days 

 after I had left the flask standing open. The vessel which I placed 

 near the apparatus contained on the following day Vibriones and 

 Monades, to which were soon added larger Polygastric Infusoria, and 

 afterwards Rotatoria. 



XVII. ON THE DEVELOPMENT OF THE VASCULAR TISSUE OF PLANTS.* 



By E. J. Quekett, Esq. F.L.S., %c. 



IN these observations it was shown that the membranous tube which 

 forms the parietes of vessels, originates from a cytoblast or nucleus, in 

 a manner similar to that described by Schleiden, in the formation of 

 ordinary cells of a plant, from which, at first, it is difficult to recognise 

 them ; but in a short period they assume the usual elongated cylindrical 

 form, and the cytoblast becomes absorbed. 



Immediately after this state, and before the fibre becomes deposited, 

 the contents of the young vessel, which appear to be gelatinous, be- 

 come charged with innumerable granules, so small as not to allow light 

 to be transmitted through them looking as blackish dots, and just 

 visible under very high magnifying powers. These granules possess 

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

 they have become a little enlarged, they begin to adhere to the 



Abstract of a paper read before the Microscopical Society of London, February 



19th, 1840. 



