Book I. DISEASES OF VEGETABLES. 259 



subjected to this operation for many successive years ; and the hole, if not very large, will close un amir, 

 like the deep incision, not by the union of the broken fibres of the wood, but by the formation onXbart 



and wood projecting beyond the edge ot the orifice, and finally shutting it up altogether 



lb/5. Girdltng is an operation to winch trees in North America are often subjected, when the firmer 

 Wishes to clear his land of timber It consists in making parallel and horizontal incisions with ainx'I 

 the trunk of a tree and carrying them quite round the stem, so as to penetrate through the alburnum in 

 then to scoop out the intervening portion. If this operation is performed earlv in the snrine and before 

 the commencement of the bleeding season, the tree rarely survives it ; though" some trees that are ne •ii 

 harly tenacious of lite, such as^Ver saccharinum and Nyssa integrifblia, have been known to survive it a 

 considerable length of time. ""' 



1676. Fracture. If a tree is bent so as to fracture part only of the cortical and woodv fibres and the 

 stem or branch but small, the parts will again unite by being put back into their natural position and well 

 propped up. Especially cure may be expected to succeed if the fracture happens in the spring • but it will 

 not succeed if the fracture is accompanied with contusion, or if the stem or branch is large • and even 

 where it succeeds the woody fibres do not contribute to the union, but the granular and herbaceous sub 

 stance only, which exudes from between the wood and liber, insinuating itself into all interstices and 

 finally becoming indurated into wood. 



1677. Pruning. Wounds are necessarily inflicted by the gardener or forester in pruning or lopping off 

 the superfluous branches; but this is seldom attended with anv bad effects to the health of the tree if done 

 by a skilful practitioner : indeed, no further art is required, merely for the protection of the tree' beyond 

 that of cutting the branch through in a sloping direction, so as to prevent the rain from lodging. ' In this 

 case the wound soon closes up by the induration of the exposed surface of the section, and by trie protru- 

 sion of a granular substance, forming a sort of circular lip between the wood and bark; and hence the 

 branch is never elongated by the growth of the same vessels that have been cut, but by the protrusion of 

 new buds near the point of section. 



1678. Grafting. In the operation of grafting there is a wound both of the stock and graft, which are 

 united, not by the immediate adhesion of the surfaces of the two sections, but by means of a granular and 

 herbaceous substance exuding from between the wood and bark, and insinuating itself as a sort of cement 

 into all open spaces : new wood is finally formed within it, and the union is complete. 



1679. Felling is the operation of cutting down trees close to the ground, which certain species will sur- 

 vive, if the stump be protected from the injuries of animals, and the root fresh and vigorous. In this case 

 the fibres of the wood are never again regenerated, but a lip is formed as in the case of pruning ; and buds, 

 which spring up into new shoots, are protruded near the section ; so that from the old shoot, ten, twelve! 

 or even twenty, new stems may issue, according to its size and vigour. The stools of the oak and ash tree 

 will furnish good examples; but there are some trees, such as the pine and fir tribe, which never send 

 out any shoots after the operation of felling. The frankincense pine is said to be an exception ; but any 

 specimens we have seen do not incline us to the belief of such an anomaly. 



1680. If buds are destroyed in the course of the winter, or in the early part of the spring, many plants 

 will again generate new buds, which will develope their parts as the others would have done, except that 

 they never contain blossom or fruit. Du Hamel thought these buds sprang from preorganised germs, 

 which he conceived to be dispersed throughout the whole of the plant; but Knight thinks he has disl 

 covered the true source of the regeneration of buds, in the proper juice thai is lodged in the alburnum. 

 Buds thus regenerated never contain or produce either flower or fruit; perhaps because the fruit-bud 

 requires more time to develope its parts, or a peculiar and higher degree of elaboration ; and that this 

 hasty production is only the effect of a great effort of the vital principle for the preservation of the indi- 

 vidual, and one of those wonderful resources to which nature always knows how to resort when the vital 

 principle is in danger. But though such buds do not produce flowers directly, as in the case of plants 

 which bear their blossoms on last year's wood ; yet they often produce young shoots which produce blos- 

 soms and fruit the same season, as in the case of cutting down an old vine or pruning the rose. 



1681. Sometimes the leaves of a tree are destroyed partially or totally as soon as they are protruded from 

 the bud, whether by the depredations of caterpillars or other insects, or by the browsing of cattle. But if 

 the injury is done early in the spring, new leaves will be again protruded without subsequent shoots. 

 Some trees will bear to be stripped even more than once in a season, as is the case with the mulberry tree, 

 which is cultivated in the south of France and Italy for the purpose of feeding the silkworm ; but if it be 

 stripped more than once in the season, it requires now and then a year's rest. 



1682. The decortication of a tree, or the stripping it of its bark, may be either intentional or acci- 

 dental, partial or total. If it is partial, and affects the epidermis only, then it is again regenerated, 

 as in the case of slight incision, W'thout leaving any scar. But if the epidermis of the petal, leaf, or 

 fruit is destroyed, it is not again regenerated, nor is the wound healed up, except by means of a scar. 

 Such is the case also with all decortications that penetrate deeper than the epidermis, particularly if the 

 wound is not protected from the action of the air. If the decortication reaches to the wood, then new 

 bark issues from between the bark and wood, and spreads till it covers the wound. But the result is not 

 the same when the wound is covered from the air. In the season of the flowing of the sap Du Hamcl 

 detached a ring of bark of three or four inches in breadth, from the trunks of several young elm trees, 

 taking care to defend the decorticated part from the action of the air, by surrounding it with a tube of 

 glass cemented above and below to the trunk. After a few days the tubes became cloudy within, par. 

 ticularly when it was hot ; but when the air became cool, the cloud condensed and fell in drops to the 

 bottom. At last there began to appear, as if exuding from between the bark and wood of the upper part 

 of the wound, a sort of rough scurfy substance ; and on the surface of the wood, as if exuding from be- 

 tween the longitudinal fibres of the alburnum, a number of gelatinous drops. They were not connected 

 with the scurfy substance at the top, but seemed to arise from small slips of the liber that had not been 

 completely detached. Their first appearance was that of small reddish spots changing by degrees into 

 white, and finally into a sort of grey, and extending in size till they at last united and formed longitudinal 

 ridges, which constituted a new bark. 



1683. Abortion or failure in the produce of flowers, fruits, or of perfect seeds, is generally the effect of 

 accidental injuries, either directly to the flower or fruit, by which they are rubbed off or devoured by 

 insects ; or to the leaves by insects; or to the roots by exposure to the air or cutting off so much of them 

 as essentially to lessen their power of drawing up nourishment. Other causes will readily suggest them- 

 selves ; and one of the commonest, as to seeds and fruits, is want of sufficient impregnation. 



168+. Premature flowering or fruiting is sometimes brought on by insects, but more generally by 

 checks produced by cold, or injuries from excessive heat, or long-continued drought. Fruit is often 

 ripened prematurely by the puncture of insects ; and a pine-apple plant of almost any age may be thrown 

 into fruit by an hour or two's exposure to a frosty atmosphere in winter, or by scorching the roots in an 

 overhot tan-bed at any season. 



Sect. II. Diseases. 



1685. Diseases are corrupt affections of the vegetable body, arising from a vitiated 

 state of its juices, and tending to injure the habitual health either of the whole or part of 

 the plant. The diseases which occur the most frequently among vegetables are the fol- 

 lowing : — Blight, smut, mildew, honey-dew, dropsy, flux of juices, gangrene, etiolation, 

 suffocation, contortion, consumption. 



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