PLANTING. 71 



is destroyed by it. When there is made a strong effort of the functions of 

 the plant to heal up the wound, and, after it is almost wholly closed with 

 healthy bark, a substance of a dark colour and resinous appearance is 

 exuded. This substance is termed ulmin ; as a pigment it produces 

 the most beautiful brown, and appears to consist of a peculiar extractive 

 matter and potassa*. The oak, under the like circumstances, exudes a 

 substance having similar external characters. The birch and maple, 

 when cut or lacerated through the bark into the wood, suffer much from 

 the loss of sap which flows from such wounds. 



The pine and fir tribe of trees have a resinous juice, which exudes freely 

 from wounds of the bark. When large branches are injudiciously pruned 

 off, the injury is considerable from the waste of sap. In the cases of full- 

 grown trees of the elm being affected with this disease, the best course is 

 to take them down for timber ; but where it is desirable to preserve the 

 tree for landscape or ornamental effect, the decayed stumps should be cut 

 away close to the sound bark, and the wound dressed carefully to protect 

 it from the weather. If a cavity exists out of which the sap has, for a con- 

 siderable period, been in the habit of exuding, the aperture should be 

 cleared of the dead bark covering its sides, and then the mouth should be 

 securely closed by the composition before recommended, or by any other 

 substance that may be found more effectual to prevent the admission of 

 rain, and of air. Whatever tends to increase the number of healthy branches 

 and leaves on the tree, will the most effectually restrain the disease. 



Tabes, or the wasting of trees, is brought on not unfrequently by para- 

 sitical plants, as ivy, covering the cutis of the barks, and preventing the 

 healthy functions of that organ. The loss of the green colour of the 

 leaves, the gradual wasting of the branches, and diminution of the 

 foliag-e, indicate the confirmation of the disease. If taken in time the 

 remedy of cutting the ivy at the root is speedy and effectual. When 

 lichens pervade not only the stems but the branches of trees, the functions 

 of the bark are disturbed, and disease ensues. On damp soils, where 

 proper thinning is neglected, lichens and mosses propagate to the ex- 

 tremities of the branches, and flourish in a surprising degree. Caustic 

 lime water thrown upon the parasites will destroy them without injuring 

 the tree, provided it be done during the fall of the leaf. A hand-engine 

 will apply the lime water to a great many trees in the course of one day. 

 The necessity of topical applications, however, of this sort for forest-trees, 

 ought to be avoided by timely thinning and pruning, thereby admitting 

 a circulation of pure air, and the solar rays into the interior of the planta- 

 tion, which check the propagation and growth of parasites. 



The number of different species of insects which infest forest-trees is 

 very great; they are all productive of more or less injury to the growth of 

 the plants. The most destructive are : the^ppear. 



*Noctuapinastri,1u{n. xyle?ia, Hub. pine moth June. 



fimbria oak moth . August. 



pyramided copper underwing oaks 



macilenta brickmoth elms 



citrago sallow moth limes 



alniaria canary-shouldered moth limes 



erosaria . . . limes September. 



olivaria green carpet moth birch August. 



be.tulitana . . 



* Agricultural Chemistry, p. 105. Ulmin is elsewhere stated to be an acid sui generis, 

 and, like other vegetable acids, to be a compound of carbon, hydrogen, and oxygen that 

 it combines with potassa like an acid ; and is again precipitated from it by acids having a 

 stronger affinity for potassa. 



