100 ACCOUNT OF SOME EXPERIMENTS ON THE 



such branches will be similar to that of the trunk ; and the growth of 

 the insulated tree on the mountain will be, as we always find it, low and 

 sturdy, and well calculated to resist the heavy gales to which its situation 

 constantly exposes it. 



Let another tree of the same kind be surrounded, whilst young, by 

 others, and it will assume a very different form. It will now be deprived 

 of a part of its motion, and another cause will operate : the leaves 

 on the lateral branches will be partly deprived of light, and, as I have 

 remarked in the last paper I had the honour to address to you, little 

 alburnum will then be generated in those branches. Their vigour, of 

 course, becomes impaired, and less sap is required to support their 

 diminished growth; more, in consequence, remains for the leading 

 shoots ; these, therefore, exert themselves with increased energy ; and 

 the trees seem to vie with each other for superiority, as if endued with 

 all the passions and propensities of animal life. 



An insulated tree in a sheltered valley will assume, from the fore- 

 going causes, a form distinct from either of the preceding* ; arid its 

 growth will be more or less aspiring, in proportion to the degree of pro- 

 tection it receives from winds, and its contiguity to elevated objects, by 

 which its lower branches, during any part of the day, are shaded. 



When a tree is wholly deprived of motion, by being trained to a 

 wall, or when a large tree has been deprived of its branches, to be 

 regrafted, it often becomes unhealthy, and not unfrequently perishes, 

 apparently owing to the stagnation of the descending sap, under the 

 rigid cincture of the lifeless external bark. I have, in the last two years, 

 pared off this bark from some very old pear and apple trees, which had 

 been regrafted with cuttings from young seedling trees, and the effect 

 produced has been very extraordinary. More new wood has been 

 generated in the old trunks, within the last two years, than in the pre- 

 ceding twenty years ; and I attribute this to the facility of communica- 

 tion which has been restored between the leaves and the roots, through 

 the inner bark. I have had frequent occasion to observe, that wherever 



* Not only the "external form of the tree, but the internal character of the wood, will be 

 affected by the situation in which the tree grows ; and hence, oak timber which grew in crowded 

 forests appears to have been mistaken, in old buildings, for Spanish chesnut. But I have 

 found the internal organization of the oak and Spanish chesnut to be very essentially different. 

 (See a magnified view of each in plate 5.) 



The silver grain and general character of the oak and Spanish chesnut are also so extremely 

 dissimilar, that the two kinds of wood can only be mistaken for each other by very careless 

 observers. Many pieces of wood found in the old buildings of London, and supposed to be 

 Spanish chesnut, have been put into my hands ; but they were all most certainly forest oak. 



