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By outer bark, then, I mean not only the transverse, but also a part, less or more, of the longitudinal, except that very thin, smooth part next the wood, which remains entire when the trees burst their bark,
Whether the longitudinal is all one bark, or more, I have not made it my study to determine: but a separation or division can very easily be made, and is frequently made by nature. I have, however, to avoid circumlocution, been under the necessity of dividing it into two, which I have distin.
guished by inner and inmost.
By inner bark I mean less or more of the longitudinal, except the inmost, by which I mean that very thin smooth part next the wood, which remains entire when the trees burst their barks, either by nature, or when
* assisted by art. This inmost bark appears to be, in some respects, very similar to the periosteum in the animal body, and might not improperly be called the periligneum. It resists putrefaction to a high degree, and remains sound long after all the rest of the bark is completely rotten. It possesses a considerable degree of elasticity, which is the cause of its remaining entire when the inner bark rends, and by this quality yields
to the circulation of the sap.
By transverse bark, I mean that external thin membrane whose fibres run across the
tree, by some called Epidermis.
When I use the word peeling, it is to be understood I mean taking off the outer bark
as above defined.
MEANS OF PREVENTION AND CURE.
This subject, which has attracted so much attention, and undergone so much investigation, seems still involved in great obscurity. If my observations can throw any light
upon it, or tend to lead others to any useful discovery, I shall consider my pains well
bestowed, and myself amply rewarded.
The first thing necessary to be done, is
to investigate the causes.
The principal of these appear to me to be Vermin, Constriction of the Bark, and
These causes, though they may exist separately, are often combined together, and
depend for their continuance and extension
on one another.
As the first of these causes, viz. Vermin, appears to be the most common and most general, and likewise as the other causes
will, in a great measure, be obviated by the
mode of treatment I propose for this, I shall begin with it.
When fruit trees grow old, the outer bark cracks and rends into thousands of fissures and crevices, where the vermin deposit their ova, which, coming to life in the spring, attack and destroy first the blossom and leaves of the small short branches on the trunk, and large branches, and soon ex
tend their depredations over the whole tree.
From this will be seen the reason why fruit trees are so often barren near the trunk, and bear only on the extremities of the branches, and frequently on the upper branches only. For, though the progress of the vermin is very rapid, yet, in fine weather, the fruit on the extremities will
get set before they reach it.