334 



THE AGRICULTURAL NEWS. 



October 14, 19n. 



FUNGUS NOTES. 



WOUNDS IN PLANTS AND THEIR 



TREATMENT. 



PART I. 



TTnder the term Wound is included any destruction or 

 removal of the living tissues of plants, whether by natural or 

 artificial means. All plants who.se aerial structures endure 

 for any length of time are provided with a hard, dry outer 

 covering layer, which serves to protect the inner tissues from 

 the attacks of other plants, such as fungi, and of some, at any 

 rate, of the members of the animal kingdom. In trees 

 and shrubs belonging to the great class of Dicotyledons, 

 this covering is known as the bark. It arises through 

 the activity of a special layer of growing cells situated in the 

 cortex. This layer gives rise to two kinds of cells. On the 

 inside new living cortical cells are formed, on the outside 

 cork cells are produced. These have special walls which are 

 impervious to the passage of Avater, and, in consequence, the 

 cells outside of them die. The mass of dry, thick-walled cells 

 serves, however, to protect the inner tissues, since it is resist- 

 ant to the attacks of bacteria and fungi, which can destroy 

 readily the soft-walled living cells. Soft green plants and 

 parts of plants are protected by the outer thick wails of the 

 cells composing the skin or epidermis, but this protection is 

 not so thorough as is that afforded by the bark. 



It will now be apparent that the chief danger to plants 

 attendant upon wounding, is the exposure of the inner unpro- 

 tected tissues to the attacks of parasites, which may ultimatel}' 

 cause their death. In order to obviate this, dicotyledonous 

 plants attempt to re-cover the wound with bark, ajid the 

 degree of succe.ss attendant upon this endeavour depends 

 largely upon the size of the wound, its nature, and the general 

 conditions to which the plant is subjected. The covering is 

 formed by the growth of the cambium at the edge of the 

 wound, by which means a plate of tissue is produced which 

 extends totally or partly over the exposed surface. This 

 plate is known as a callus. 



Natural wounds are those caused by the falling of leaves, 

 fruit or twigs, when these arc purposely cut off by the plant 

 itself. They do not form a source of danger to the tree, .since 

 prior to the fall of the parts removed, a special corky layer 

 is produced over the inner tissues, which their disappearance 

 would otherwise leave expo.sed. 



Artificial wounds are due to several causes, among them 

 may be mentioned the action of wind, of animals of all kinds 

 including man, and of other plants, such as fungi. They 

 comprise all wounds made in pruning or in removing diseased 

 tissue. 



iNTKNTiiiNAT, WOUNDS. Under this bead are included all 

 wounds made in pruning or in removing dead or dying parts 

 of plants. Such wounds are often necessary for various 

 reasons, though it is undoubtedly a great mistake to prune 

 more than is absolutely required for the best growth and 

 development of the plants; or in the case of trees grown in 

 cities, for the convenience of the general public. In the case 

 of permanent crops in particular, such for example as cacao, 

 limes and Para rubber, the extent of the pruning given should 

 never be greater than is shown by experience to be inevitable, 

 and the operation itself should be conduclcd with all due care. 



In the old days, before the principles underlying careful 

 pruning were fully understood, little attention if any was 

 paid to the method emjtloyed. At the present time, however, 

 certain fundamental principles are fully recognized. In the 



first place, it has been found that trees can entirely cover 

 over any wound, caused by the removal of a branch up to 4 

 inches in diameter, if it is cut off" so that the exposed wood 

 presents a smooth surface flush with, and parallel to, the bark 

 of the trunk. Small branches should, therefore, be removed 

 with a saw as close to the surface from which they arise as is 

 possible, the cut passing through the bulge at the base of the 

 branch. The surface may then be furnished with one of the 

 protective coverings which are described below. This \iTe- 

 vents the entry of organisms causing disease, until the bark 

 has entirely covered the wound. 



When a large, heavy branch has to be removed, it is not 

 safe to commence sawing it away directly. If this is done, the 

 branch often Iireaks from its own weight and tears a large 

 portion out of the stem, making an ugly irregular wound 

 that is difficult to protect. To avoid this, a cut should first 

 be made on the under side of the branch at aljout 1 foot 

 from the stem and extending nearly half-way through the 

 branch. Then a second cut should be made on the upjier 

 surface about 3 inches further from the stem, and should 

 be continued until the branch falls off. Finally the stub 

 should be cut off flush with the stem. The exposed surface 

 must then be protected as is mentioned below. 



Another kind of wound involving an actual cutting 

 into the tree may be necessary when diseased patches such as 

 are caused by canker have to be excised, or when boring 

 insects like the cacao beetle have to be removed. Such 

 excisions should be done with a chisel or gouge and a mallet; 

 all diseased tissue should be cut out and the treated .surface 

 smoothed off and covered. 



covERixc. wou^'ns Various preparations have been 

 recommended for protecting cut surfaces. One of those in 

 most general u,-5e is, perhaps, tar. Ordinary coal tar is the 

 only form that can be recommended; Stockholm tar is too 

 thin and evanescent. Tar has, however, one drawback, 

 namely that ic kill.^ the tissues round the edge of the wound 

 and thus delays healing, while it also kills portions of the 

 bark if it is allowed to drip on to them. A better substance 

 is resin oil, which does not appear to exercise any harmful 

 effect on living tissues. The drawback to this is that it 

 cannot be seen easily what wounds have, and what have 

 not, been treated. This difficulty may be overcome by 

 mixing 4 parts of the oil with one of tar, when the tar 

 renders the treated wounds readily distinguishable. (See 

 Agricultural News, Vol. VIII, p. Gl.) An excellent substance 

 for covering wounds that are expected to heal over entirely is 

 a mixture of '1 parts of clay and one of cow dung, with the 

 addition of a little hair. If the entrance of woodlioring 

 beetles is feared, a few drops of carbolic acid should be added 

 to the mixture. Another covering substance that has given 

 good results is white paint, while fetch suggests the applica- 

 tion of the sediment formed when Bordeaux mixture is 

 allowed to stand; this should be applied in a layer about 

 i-inch thick. Vet another nixlurc is stated by Petch to have 

 been recommended in Germany as a cheap protective for large 

 wounds, and has been subjected to experiment there. It 

 consists of 500 grams of melted white resin, 500 grams of 

 wood tar, 125 grams of printers' varnish (linseed oil varnish), 

 and 30 grams of spirit. 



Large wounds caused by the removal of big branche.s or 

 the excision of cankered areas cannot be expected to heal over 

 entirely. I'etch suggests the following treatment in such 

 cases. Hound the edge of the wound over a strip 1 inch 

 in width, which is likel}' to lieconie covered by the wound 

 callus, the mixture of clay and cow dung should be applied. 

 The central portion .should then be covered over with tar, 

 resin oil, or one of the other substances mentioned aliove. 



