150 VEGETABLE ORGANOGRAPHY. 



light, in the most evident manner, a contrary proposition 

 to that of Duliamel ; that is to say, the non-disappearance 

 of the pith in old trunks. Their testimony is confirmed 

 by Desfontaines, Jussieu, and Labillardiere, who have 

 found the pith in old trunks of the Hawthorn, Beech, 

 Elder, Oak, and Elm; and I have myself verified it in 

 several trees, such as the common Chestnut and the 

 Ailanthus. 



How then is it that a question, in appearance so 

 simple as that of knowing whether or not there is any 

 pith in old trunks, has been for so long a time a subject 

 of doubt and uncertainty ? It is that it has not been suf- 

 ficiently remarked, that all young branches have not a 

 "uniform diameter, and that their medullary canal is in 

 proportion to their size : thus, for example, the strong 

 young branches of the Elder have a pith, the diameter of 

 which is at least double that of the fruit-bearing branches. 

 Du Petit-Thouars has also remarked, that in the young 

 branches of this tree, the diameter of the pith varies in 

 different proportions, from one to nine lines. These 

 variations are found in almost all trees ; so that if we 

 were to examine a very large young shoot, and after- 

 wards a branch proceeding from a slenderer young 

 shoot, we should decide that the pith has diminished, 

 exactly as we would decide the contrary if we compared 

 a very slender young shoot, with a branch produced by 

 a very vigorous one. The very hard trunks in which 

 the medullary canal is scarcely visible, proceed from 

 branches which, in their young state, had an extremely 

 small pith. Those with a visible pith proceed from 

 branches which had, in their young state, an abundant 

 pith ; and the same tree sometimes presents these two 

 kinds of branches. 



If so simple a fact as the existence or the disappear- 

 ance of the pith in old trunks be disputed, we know 



