FUNCTION. 1 OF TISSUES. 163 



" In the manuals which treat of organic chemistry, we 

 generally find woody fibre treated of as a proximate element 

 amongst the indifferent vegetable substances, along with 

 starch, gum, sugar, &c. It is only lately that Reade has 

 endeavoured to earn the merit of analysing the different 

 forms of organised vegetable substances when separated, but 

 I doubt whether anything available for science has resulted 

 therefrom. I will, however, in no wise intimate that Mr. 

 R-eade has not made use of really isolated spiral vessels in 

 his analysis, since he expressly asserts it; but he does not 

 once mention the remotest attempt to separate the interior 

 matter from the cells and vessels, which necessarily must have 

 been done if any value were to be attached to the result of 

 the elementary analysis. 



" This question arises with every one who knows that the 

 greater part of vegetable tissue consists of a pellucid mem- 

 brane, and the formations deposited on its inner surface : 

 Are this membrane and the subsequent deposits formed of 

 the same chemical substance ? In fact, as we know from 

 Mohl and Meyen that the increased thickness of the walls of 

 cells consists of several layers, that even the spiral fibres are 

 composed of an original fibre, and a subsequently deposited 

 covering surrounding it, which I have found confirmed in 

 innumerable instances, the further question arises whether 

 both the single layers of incrustation, and the (additional ?) 

 parts of the spiral fibres, are not different from each other. 

 As there can be no mechanical separation of such closely 

 combined and microscopic parts, nothing can be done fur- 

 ther than to superadd to chemical examination the use of 

 the microscope, and by this means to observe the action 

 of chemical reagents on the different elementary parts of the 

 vegetable structure. 



" I. I had made fine sections of an internodium of Arundo 

 Donax an inch in diameter, and boiled them for some 

 minutes in a solution of caustic potash. On bringing the 

 section again under the microscope I was surprised by a 

 peculiar appearance. A few ringed and spiral vessels were 

 cut through, so that one could plainly see the section of their 

 very thick fibre. By the boiling in caustic potash the spiral 



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