41 



plants upon which more different opinions have been formed than 

 these stomates." Professor Lindley himself, for instance, supported 

 by Decandolle, Adolphe Brongniart and Link, recognizes them as 

 openings. Other anatomists of high reputation entertain a directly 

 opposite opinion, and deny the existence of passages. Dr. Brown 

 describes them as glands, really almost always imperforate, with a 

 disk formed by a membrane of greater or less opaqueness. It would 

 doubtless be great presumption in me to say that the opinions of all 

 these eminent observers are wrong ; nevertheless, I cannot say, with 

 the example of the rhubarb before me, that any one is exactly right. 

 Those who deny, in toto, the existence of apertures, or suspect the 

 openings to be an optical deception, are unquestionably in error. 

 Professor Lindley seems almost to doubt whether Dr. Brown has suffi- 

 ciently established the existence of the membrane overlying the aper- 

 tures ; and Dr. Brown makes the perforations the exception, and not 

 the rule. One thing, however, is clear, from this contrariety of opin- 

 ion, that the ordinary mode of microscopic examination, which has 

 led so many naturalists to different and opposite conclusions, must 

 fail in the case before us. And indeed, the fact is, that the tissue in 

 question is of so delicate a nature that an observer might be pardoned 

 if he either considered the supposed openings to be spaces more pel- 

 lucid than the surrounding tissues, or if he confessed at once, with the 

 celebrated Grew, that he had no exact idea of their structure. 



The application of the process of charring will be found to throw 

 great light upon the whole subject. From its very nature it will act 

 upon the vegetable tissue, but upon that only ; and will consequently 

 discover, with the utmost exactness, every the most minute perfora- 

 tion. At the same time it will not fail to enable us to detect the most 

 delicate portion, and the precise position and character of this natu- 

 rally colourless membrane. Accordingly, the examples which will be 

 submitted to actual inspection — "oculis subjecta Jidelibus" will esta- 

 blish the following facts : — 



That in the simple uncharred state of the semi transparent tissue 

 there is much room for difference of opinion, so that the eye, fortified 

 by a little previous theory, might most pardonably see the stomata 

 either open or closed. 



That the application of the process of charring proves, beyond a 

 doubt, that the stomata in this tissue of the rhubarb are distinct open- 

 ings into the hollow chambers of the parenchyma of the leaf. 



That the perforation is the rule and not the exception in the 

 structure. 



