OF PLANTS. 291 



perish. When the bark cracks, becomes liard and scaly, 

 without this flowing of resin, it seems to suffer these injuries 

 either from being exposed to too powerful a heat ol' the sun, 

 from the influence of too dry seasons, or of too barren a soil. 

 The leprosy or scab which we have mentioned, destroys 

 the Olive-trees in Italy ; (Giovene in Opuscoli scelti, xiii. 

 p. 106.) In our Cherry trees, the Spharia pidchella lodges 

 between the torn rind and the inner bark. But slill worse 

 guests are the earwigs, the wood wasps, and the drilling 

 worms, which often make long excavations under the rind, 

 and thus become injurious to the life of the stem, 



420, 



A superabundance of raw j uice in trees, which have been 

 rendered feeble by management or weak by frost, produces 

 the dropsy or jaundice. The bark becomes spongy, and, 

 when pressed, gives out a great quantity of water ; the young 

 shoots are thin and powerless, the leaves pale and yellow, and 

 fruit is seldom produced. Stimulating and powerful nourish- 

 ing matters from animal dung, mud, lime, and even soot, when 

 they are applied in time, take away the disease, and shew the 

 correctness of the explanation we have given of it. 



AVe may attribute in some measure to the same cause 

 the debility of the alburnum in forest trees ; because, where- 

 ever it occurs, either early frost, or other weakening causes, 

 have prevented the concentration of the sap, and the proper 

 formation of wood; the unformed sap thus remains in the 

 alburnum, (^98.) ; (Mezieres, De la Force de Bois, p. 94 ; 

 Slevogt, in Laurop's Annalen.) 



421. 

 We meet with blotches and canker, as diseases of trees, the 

 former of which are manifested by dark spots in the rind and 

 wood, and commonly have their origin in the sterility of tlie 

 soil, and in other enfeebling causes. This disease chiefly lays 

 waste the Mulberry trees in Italy, and has given rise to 

 manifold and very anxious investigations ; (Scoj)()li, Ann. 



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