282 Mr. Knight’s Account of some Experiments 
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 en- 
dued with all the passions and propensities of animal life. 
An insulated tree in a sheltered valley, will assume, from the 
foregoing causes, a form distinct from either of the preceding ;* 
and its growth will be more or less aspiring, in proportion to 
the degree of protection it receives from winds, and its con- 
tiguity 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 unfre- 
quently 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 pro- 
* 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 IV-)' 
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. 
