CAN 



[ 188] 



CAN 



people," it may be determined as to its 

 point of attack by the irritability of that 

 part of the system. 



This disease commences with an en- 

 largement of the vessels of the bark of a 

 "branch or of the stem. This swelling 

 invariably attends the disease when it 

 attacks the apple-tree. In the pear the 

 enlargement is less, yet is always pre- 

 sent. In the elm and the oak some- 

 times no swelling occurs; and in the 

 peach we do not recollect to have seen 

 any. The swelling is soon communi- 

 cated to the wood, which if laid open 

 to view on its first appearance by the 

 removal of the bark, exhibits no marks 

 of disease beyond the mere unnatural 

 enlargement. In the course of a few 

 years, less in number in proportion to 

 the advanced age of the tree, and the 

 unfavourable circumstances under which 

 it is vegetating, the swelling is greatly 

 increased in size, and the alburnum has 

 become extensively dead ; the bark above 

 it cracks, rises in discoloured scales, and 

 decays even more rapidly than the wood 

 beneath. If the canker is upon a mo- 

 derately-sized branch, the decay soon 

 completely encircles it, extending through 

 the whole alburnum and bark. The cir- 

 culation of the sap being thus entirely 

 prevented, all the parts above the disease 

 perish. 



Trees injudiciously pruned or growing 

 upon an ungenial soil are more frequently 

 attacked than those which are advancing 

 under contrary circumstances. The 

 oldest trees are always the first attacked 

 of those similarly cultivated. The 

 golden pippin, the oldest existing va- 

 riety of the apple, is more frequently 

 and more seriously attacked than any 

 other. The soil has a very considerable 

 influence in inducing the disease. If 

 the subsoil be an irony gravel, or if it 

 is not well drained, the canker is almost 

 certain to make its appearance amongst 

 the trees they sustain, however young 

 and vigorous they were when first 

 planted. 



Bruises and wounds of all kinds 

 usually are followed by canker in the 

 wounded part, if the tree is tending to 

 this disease. 



All these facts before us unite in as- 

 suring us that the canker arises from 



the tree's weakness, from a deficiency 

 in its vital energy, and consequent in- 

 ability to imbibe and elaborate the 

 nourishment necessary to sustain its 

 frame in vigour, and much less to supply 

 the healthy development of new parts. 



It is quite true that over-luxuriant 

 trees are particularly liable to this dis- 

 ease ; but over-luxuriance is really a 

 demonstration that the tree does not 

 digest and secrete its juices healthily. 



If over-luxuriance threaten to intro- 

 duce canker, the best remedy is to re- 

 move some of the main roots of the 

 tree, and to be particularly careful not 

 to add any manure to the soil within 

 their range. On the contrary, it will be 

 well if the continued exuberant growth 

 shows the necessity for the staple of the 

 soil to be reduced in fertility by the 

 admixture of one less fertile, or even of 

 drift sand. If there be an excess of 

 branches, the saw and the pruning-knife 

 must be gradually applied. It must be 

 only a tree of very , weak vital powers, 

 such as is the golden pippin, that will 

 bear the general cutting of the annual 

 shoots. A vigorous variety would ex- 

 haust itself the following year in the 

 production of fresh wood. Nothing 

 beyond a general rule for the pruning 

 can be laid down ; keep a considerable 

 vacancy between every branch, both 

 above and beneath it, and especially 

 provide that not even two twigs shall 

 chafe against each other. The greater 

 the intensity of light, and the freer the 

 circulation of air amongst the foliage of 

 the tree, the better the chance for its 

 healthy vegetation. If the disease being 

 in a fruit tree be a consequence of old 

 age, it is probably premature, and in- 

 duced by injudicious management, for 

 very few of our varieties are of an age 

 that insure to them decrepitude. We 

 have never yet known a tree, unless in 

 the last stage of decay, that could not 

 be greatly restored by giving it more air 

 and light, by careful heading in pruning, 

 improvement of the soil, and cleansing 

 the bark. 



If the soil by its ungenial character 

 induces the diseases, the obvious and 

 only remedy is its amelioration ; and if 

 the subsoil is the cause of the mischief, 

 the roots must be prevented striking 



