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I, — On the Development of the Vascular Tissue of Plants. By Edwin J. 

 QUEKETT, F.L.S., B.S., &c. 



Mr. Quekett commences his paper by commenting on the difficul- 

 ties attendant on the enquiry ; and observes that he believes the idea 

 to be in great measure correct, that " in structure vessels differ but 

 little from cellular tissue, and that the elements of which the latter is 

 formed are only altered and converted to fulfil a different function in 

 the former, and that the development of the one will more or less cor- 

 respond to that of the other." He then proceeds to give the views of 

 Schleiden, Raspail, &c., and alludes to the opinion of Mirbel, Trevi- 

 ranus and Slack, that the membranous tube of a vessel is formed firom 

 a number of cells ranged end to end, their connexions being ultimate- 

 ly absorbed, thus causing the production of a continuous cylinder in- 

 stead of several separate cavities. Pursuing this idea the author thus 

 proceeds : — 



" I must state that in many instances I have met with arrangements of cells in 

 such a way as would lead one to suspect that this was the true origin of a vessel ; and 

 it is a curious fact that cells adhere end to end much more strongly than they do side 

 by side ; therefore, when disturbed, they appear more frequently in strings than in other 

 forms : but I believe no one has ever seen the fact farther than here described, or fol- 

 lowed out the complete development of a vessel from this condition of cells ; and there 

 is one fact presently to be mentioned, connected with the development of a vessel, 

 which entirely disproves this theory." — p. 3. 



In order to watch the development of the membranous tube of a 

 vessel, Mr. Quekett recommends that some part of a plant in a nascent 

 state, as a bud or bulb, should be selected for examination ; he also 

 lays great stress on the necessity there is for caution in making dis- 

 sections of recent paits in order to witness the appearances which he 

 subsequently describes. The author then details observations for the 

 most part confirmatory of Schleiden's views, as explained by that 

 writer in his memoir on Phy togenesis, a translation of which appeared 

 in the ' Annales des Sciences Naturelles,' (tom. xi. Botanique) : he 

 continues : — 



" When the young vessels are recognized (which by experience becomes an easy 

 matter, even in parts considerably developed, though not so at first), they appear as 

 pellucid glassy tubes, with a cytoblast in some part of their interior ; earlier than this 

 they are not to be recognized readily from cells. As they grow older the cytoblast di- 

 minishes, and the contents, which at first were clear and gelatinous, become less trans- 

 parent from containing thousands of granules, which are too small to allow of the 

 passage of light, and consequently appear as dark points ; these atoms are about the 

 55505 of an inch in diameter, and have the motion known as " active molecules." If the 

 vessel be wounded at this period the gelatinous contents pour slowly out, and then the 



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