70 PLANTING. 



certain period of existence, in which the stages of growth are distinctly 

 marked, from the first development of the plant in its seedling state, until 

 its ultimate decay by the course of nature. Different species of trees have 

 different periods of existence. The oak is considered to be of the longest 

 duration, and, perhaps, the larch of the shortest. The oaks in Woburn 

 Park, mentioned at page 50, as being of such large dimensions and in per- 

 fect health, cannot be supposed to be under three hundred years of age. 

 The elm may be placed next in order with the chestnut, ash, beech, and 

 hornbeam, the pine, and lastly the larch*. These estimates of the compa- 

 rative duration of different species of trees are, however, given from 

 observation only, and are not founded on such certain data as to render 

 them more than an approximation to the truth ; for soils, local climates, 

 and the various other causes which promote or retard the progress of 

 vegetable health and growth, interfere with the completion of the perfect, 

 natural term of vegetable life in numerous instances. Under the most 

 favourable circumstances, however, of soil and culture, trees are subject to 

 various diseases and accidents, and from what has already been mentioned, 

 as to their structure and living functions, this will be no matter of surprise. 

 The diseases of forest-trees may be comprised under those of a general 

 nature, wherein the internal functions are interrupted or partially de- 

 stroyed ; and secondly, those of a local nature arising from external 

 causes, as accidents of various kinds, and the attacks of insects. Neglect 

 of judicious planting and of after culture, are the chief causes of the first 

 mentioned kinds of disease, and tend to aggravate the bad effects of other 

 accidents. When a tree puts forth leaves of paler tint than their natural 

 green colour, and never assumes it again during that and succeeding sea- 

 sons, and when the growth of the branches is very small and frequently 

 imperceptible, some of them also decaying at the extremities, the disease 

 is termed chlorosis. It originates principally from an ungenial subsoil. 

 The effects of confined air by a crowded state of the plantation, or a too 

 sudden exposure to sharp blasts, will also induce this disease. Topical 

 remedies are of no use, and the means of prevention should be used in 

 planting, and in the after culture. 



Spontaneous bleeding, or great loss of sap, generally ends in the disease 

 termed tabes, which, when once confirmed, is incapable of being cured. 

 The elm is of all forest-trees the most subject to this disease. Whenever 

 the branches become disproportionate to the stem and roots, or the foliage 

 too scanty to receive and elaborate the periodical flow of sap, spontaneous 

 bleeding takes place. The neglected stumps of dead brandies having 

 formed cavities, afford ready outlets to the sap. Branches which have been 

 snllered to grow too large in proportion to the rest of the tree, and are bent 

 down or project in an horizontal direction from the stem, are frequently 

 attacked with hamorrha gy , which, according to our observation and ex- 

 perience, never heals, but continues periodically until the death of the tree. 

 The tluid which is thus discharged by the elm, appears to differ in no respect 

 from the ascending sap of the plant, affording extractive and mucilaginous 

 matters, combined with potassa and lime; the solid matter deposited by 

 the fluid in its course of descent over the bark, leaves a whitish tract at 

 lii>t, but in time becomes blackened by the weather, smoke, &c. The 

 track thus marked out by the lurmorrhagr, will point out the wound with 

 certainty and readiness. (irass and herl.a^e on which this fluid drops 



i until the trees interfere with each other's healthy growth, and 



to contend i'<>r existence. Hy judicious pruning and thinning, or by keening any individual 



MI its must jH-riict healthy state, a per] ' ' v. ill be obtained, as complete as the 



I the nature of the soil \vill admit. 



* The Pi mis Lambertia before mentioned, found on the north-west coast of America, 

 was estimated of nine hundred years' growth, although sound in the timber. 



