92 Keith's Botanical Lexicon. 



bark are annually formed for a long series of years, without the 

 assistance of either leaves or descending sap of any kind ; and, 

 moreover, Mr. Keith must be aware that new bulbs and new 

 tubers are produced by old ones, without connexion with either 

 stems or foliage. Any practical man can vouch for the truth of 

 these last assertions ; and, the truth of the former, M. Dutro- 

 chet's account of the growth of the roots of the silver fir, whose 

 boles had been felled many years before, will sufficiently attest. 



This curious circumstance had been observed long before 

 M. Dutrochet published his account of it ; and it furnishes un- 

 deniable proof of the existence of a vital membrane, which 

 possesses an innate power of increasing itself, independent 

 entirely of assistance from either leaves or descending sap. It 

 is this membrane which Mr. Keith sometimes calls cambium, 

 and at other times perfect or elaborated sap; and, when de- 

 scribing it as protruding over to heal a wound, he speaks of it 

 as being granular ; which can hardly be applied with propriety 

 to either sap or cambium. 



That intelligent and practical botanist, Mr. Niven, curator 

 of the Glasnevin Botanic Garden, near Dublin, in describing 

 the new wood and bark which gradually cover a wound on the 

 stem of a tree, imagines, very properly, that the upper lip is "an 

 attempt to form roots," and that the protrusion from below is 

 " an attempt to develope shoots." That the new wood and bark 

 which cover the wound of a stem produce both roots and 

 shoots, and even flowers, is known to every pi'opagator of plants; 

 and that shoots are produced from the lower lip is admitted by 

 Mr. Keith himself, when combating the silly idea that all buds 

 originate at the pith ; which idea he repels with great truth : 

 but he appears to have some misgivings whether or not those 

 buds and shoots which come not from the pith are, or are not, 

 adventitious creations. 



Be this, however, as it may, there is no denying that both 

 roots and shoots originate on that member which is known by 

 the name of cambium in the month of May, and which is cer- 

 tainly alburnum in the following September, whether existing, as 

 it usually does, under the bark, or appearing jutting out from 

 the sides of a wound. 



Mr. Keith is well aware that the cambium appearing every 

 summer between the liber and alburnum has been considered 

 as a distinct member of exogenous stems ; and it is really a pity 

 that he has not condescended to notice and refute an opinion which 

 is at such variance with, and so antagonist to, his own physio- 

 logical principles. Errors in the science of phytology cannot 

 be too soon exposed and refuted. A silent neglect of the opi- 

 nions of obscure writers may be dignified ; but it cannot ad- 

 vance a science which is, as yet, far from being entirely free 



