SECT. II. TUBES. 35? 



by Grew and Hedwig, as visible also in the wood. 

 But I believe they have not been found in the ma- 

 tured wood, by any other vegetable anatomists. 

 Du Hamel never met with them in any of the 

 woody parts of woody plants, except in the young 

 and herbaceous branches.* Mirbel expresses him- 

 self to the same effect.^ And Mr. Knight, who 

 has examined the subject perhaps still more re- 

 cently, could not detect them in any of the per- 

 manent parts of such plants, except in the annual 

 shoot. J My own observations on this subject have 

 had nearly a similar result. Among many sub- 

 jects of examination I shall mention only the 

 Elder, Willow, Hawthorn, Cherry, and Elm-tree. 

 In the three former I found them only in the an- 

 nual shoot, situated immediately without the pith, 

 or rather imbedded in the Alburnum ; though in 

 the Elder some of them seemed to be imbedded 

 even in the pith itself. In the Cherry I found also 

 a few, very few similarly situated in the branch 

 of two years old ; but none in wood older than 

 that. And in the Elm-tree I have sometimes 

 thought I had discovered them even in the matured 

 wood. Having placed under the microscope a very 

 thin slice taken from a piece of the trunk of an 

 Elm-tree, that had been felled at least six or seven 

 years, I thought I was able to trace the remains of 

 the spiral tubes. The slice was taken from the 

 surface of a longitudinal section passing through 

 * Phys. des Arb. f Phys. Veg. vol. i. p. 67. J Phil Trans. 



