234 



LETTEES ON TREES. 



upper and the lower lips of the wound ; but, without some 

 such slight channel of union, it is contrary to experience that 

 the part of a trunk below an annual incision should increase by 

 the addition of new layers of wood until the lips of the wound 

 are united, unless buds exist upon the trunk below the ring. 

 The horizontal parenchymatous system may, however, go on 

 growing, and so form new layers. 



Dutrochet mentions some cases of extraordinary longevity 

 in the stock of Pinus Picea^ after the trunk had been felled, 

 and which he supposes fatal to the theory of wood being formed 

 by the descent of organised matter. He says that, in the year 

 1836, a stock of Pinus Picea, felled in 1821, was still alive, 

 and had formed fourteen thin new layers of wood — that is, one 

 layer each year ; and another, felled in 1743, was still in full 

 vegetation, having formed ninety-two thin layers of wood, or 

 one each year. But, it is now ascertained that these roots are 

 connected with living stems in consequence of having become 

 grafted, under ground, to the roots of the latter. 



''The observations of Mirbel on the origin of the woody 

 bundles of Palm-trees, from which it appears that the bundles 

 first appear isolated in the cellular matter of the buds, and 

 then direct themselves upwards into the leaves and downwards 

 into the trunk, are certainly opposed to the possibility of 

 regarding wood as the roots of leaves. And the difficulty of 

 admitting the theory is much increased by the existence in 

 bark of the embryo buds, already described; and by M. 

 Decaisne's statement, that in the Beet-root, when new vascu- 

 lar tissue is produced, it, in the beginning, is distinct from the 

 previously formed vascular tissue. 



'' The singular examples of carved figures being found in the 

 interior of trees also militate somewhat against the theory of 

 wood being a form of roots, and are better explicable upon the 

 supposition of a gradual superficial deposit. A very curious 

 example of this is to be found in the Gardener's Chronicle for 



