40 



VII. — The process of charring Vegetable Tissue as applied to the 

 examination of the Stomata in the Epidermis of Garden 

 Rhubarb. By the Rev. J. B. Reade, M.A., F.R.S. 



Read July 21, 1841. 



Since I first suggested the process of charring vegetable tissues, 

 with a view to a more accurate knowledge of their structure, I have 

 had many opportunities of observing the advantages of its application. 

 The well-defined form and peculiar character of the cells of cellular 

 tissue, especially when the cellules are reticulated ; the inner and se- 

 parable membrane of spiral vessels, as in the Acrocomia aculeata ; 

 the external position of the spiral thread with respect to this mem- 

 brane ; and the undoubted existence of spiral vessels in the roots of 

 many dicotyledonous plants ; — these are among the more interesting 

 examples of the success of the experiment. 



It is my present intention to do myself the honor of communicating 

 to the Microscopical Society, the result of a recent application of this 

 process to the epidermis of the leaf-sheath or ochrea of the common 

 garden rhubarb. A flower-stalk of this plant, with its beautiful and 

 well-known series of involved sheaths, out of which the clusters of 

 flowers and their basal leaves successively emerge, so entirely loses 

 the naturally strong adhesion between the subjacent cellular tissue 

 and the epidermis, if it be placed for a few days in water, that this 

 investing membrane may be readily separated by the finger from the 

 inner surface of the sheaths. Portions of this delicate tissue, of con- 

 siderable size, translucent and colourless, may thus be obtained in a 

 fit state for microscopical investigation. 



The first thing which is noticed upon examining this tissue in its 

 natural condition, a little water only being placed between the glasses 

 to prevent the loss of light consequent upon the inner reflections from 

 the surfaces of the glass, is the beautiful development of the sto- 

 mata and their surrounding concentric layers of green molecules. 

 The number of these stomata in a square inch is about 6000. They 

 are of an oval form, having, in the larger examples, a major axis of 

 ^tf of an inch, and a minor axis of about half that length. 



Stomata are described by Professor Lindley as " passages through 

 the cuticle, having the appearance of an oval space, in the centre 

 of which is a slit that opens or closes according to circumstances." 

 But it is added, — " there is, perhaps, nothing in the structure of 



