6 PLAXTIXG. 



On young shoots nml stems (he epidermis appears membraneous, or as 

 a thin transparent membrane without vessels; but late researches, aided 

 by powerful glasses, have shewn that it is partially furnished with minute 

 retiform vessels, particularly in the leaves. 



\YlitMi casually displaced off young shoots it is reproduced with little 



apparent injury to the part, unless it happen on the annual parts of the 



tree, as the leaves and ilowers. In old stems and branches the epidermis 



n attains to considerable thickness, becoming hard, rough, or granulated, 



ecu in the trunk of elm, oak, and most kinds of forest-trees, and in the 



trunk of the apricot, pear, &c., among fruit-trees. When in this latter 



state, the epidermis may be removed without injury, and, in some instances, 



it has been cleared away from these fruit trees with evident advantage to 



their general health and fertility*. 



The parenchyma is composed of hexagonal cells, containing juice, which 

 in the stems and branches is of a green colour, even when covered by a 

 thick indurated epidermis; but in the root, as before alluded to, the juice 

 of the parenchyma is colourless. 



The inner bark consists of cortical layers, constituted of longitudinal 

 fibres or vessels, which are supposed to return the sap from the leaves 

 after their undergoing certain changes by the action of solar light, heat, 

 and air. The medullary rays which pass from the pith to the cellular tex- 

 tures of the inner bark and parenchyma in a horizontal direction, appear to 

 be the medium of a lateral intercommunication of sap and air throughout 

 the entire structure of the treef. 



The green colour of the 'parenchyma depends on the exposure of its 

 epidermis to light and air; for when a portion of the stem of a tree is ex- 

 cluded from light, as is sometimes done in planting when the tree is 

 placed deeper in the soil than it stood before transplanting, the green 

 colour is destroyed in that part of it which is covered with the soil, and 

 which in course of time assumes the colour of the root; and, if much 

 moisture exists in the soil and the tree be not young, the bark so covered 

 decays, and the tree dies. Should the soil be dry, however, and the plant 



* In 1813 the following trial was made to ascertain the effects of removing the rough, 

 hardened epidermis from the trunk and limbs of a very large and aged Crassane pear- 

 .lined hori/.cmtally on a west wall, the branches extended twenty 

 a each side of the large trunk in the most perfect order. The stem v.as cleared of 

 the ro ////// epidermis entirely, and the branches on one side also were treated in like man- 

 ner. The bunches which extended on the other side of the stem, had only every alternate 

 brar.' . of the rough, hardened epidermis. Previously to this, the tree had for 



many years cea .tonally 01.. ihe extremities of the 



Tlie first se.iM.n , it'ti r the above operation, the foliage ;issiimed a more 

 ! brandies, and in the course of the second y. Mi- 

 many fruit buds were formed, which afterwards produced fruit of verv good quality. The 

 iffercd to remain with their hardened epidermis, continued barren. 

 .as another of the same species, apparently of the like age and of 

 -.amir dimensions. In this instance every second bra'nch was pruned oil' near 

 i'ts of the cr.is-.un-. cohn.ir, brown beurrie, and St. Germain, 

 i M6 grafts all succeeded so well that 



: -i fr. mi the p.-n..d <,f -raft; d ue.irly attained to the length of the 



old 1 iruit of a very superior quality. The old 



bnuic' in. lined in the same barren st.ite as before. 



Mipi-rior.it tin- end of the fifth year, in regard 



led branches ; and tin c m a like pro- 



untouched. These facts go to prove 



clearly that the thickening I the epidermis has a very considerable ill- 



flueiK 



f It is contrary I ( e.ury Knonn 1 iw of t! -r, to suppose that any part of the 



>dy can resist decomposition or decay, if it be cut oil' 

 from a reciprocal comruuuicutiun with the circulating vital juices. 



