322 Outlifies of HorticiiUnral Chemistry. 



cases, becomes obliterated, the dead layers of bark performing 

 its offices. Immediately beneath the epidermis occurs the 

 cellular integument (otherwise known as -parenchyma and jvdp). 

 It is a juicy substance, and, being the seat of colour, is analo- 

 gous to the rete mucosum of man ; which is red in the white, 

 and black in the negro. The mass of apples, &c., is com- 

 posed of it. Leaves are chiefly formed of a plate of it, enclosed 

 by epidermis. In herbs, succulent plants, leaves, and fruits, if 

 it is destroyed, like the epidermis of the same, it remains un- 

 restored ; but in the case of trees and shrubs, it is regenerated 

 after each removal. In leaves it is generally green ; in flowers 

 and fruits, of every hue. It is always cellular, and evidently 

 acts a part in the secretory system of plants. 



Under the cellular integument occurs the hark, which, in 

 annual plants, or branches of one year's growth, consists of a 

 single layer, scarcely distinguishable from the wood ; in older 

 stems and branches, it is composed of as many layers as they 

 are years of age. It is in the innermost of these, which is 

 called the liber, that the vital returning circulation and secre- 

 tions are carried on for the time being, almost exclusively. 

 These layers are concentric, or, as they are usually termed, 

 cortical layers; they are thicker in feeble plants than in more 

 vigorous ones of the same species ; they are formed of waving 

 longitudinal fibres, the meshes of the network they thus con- 

 stitute being filled with pulp. If the outer bark is destroyed, 

 but the wound does not penetrate below the liber, the wound 

 is healed up, otherwise the removed part is unregenerated. In 

 some roots, though only annuals, the bark is composed entirely 

 of liber, and is very thick, as in the carrot and parsnep, in 

 which it is evidently separated, by a light-coloured annular 

 mark, from the central or woody part. The liber is composed 

 of various longitudinal tubes, in which the true sap of the in- 

 dividual descends after elaboration in the leaves ; consequently, 

 here are found the substances that are the peculiar products 

 of each in the most concentrated state, as the resin of the fir, 

 the bitter principle of the Cinchona, or Peruvian bark, &c. I 

 will here pause, to remark upon some of the remedies which 

 have been recommended for the removal of insects from the 

 bark of trees. Oil has been directed to be smeared over them, 

 for the destruction of the A^phis lanigera, moss, &c. Whether 

 it will answer such purpose I will not stop to argue, but will 

 content myself with observing that a more deleterious appli- 

 cation is impossible : for, on the same principle that it destroys 

 the parasites, namely, by closing their spiracles and pores, and 

 thus suiFocating them, it, in a like manner, clogs up the pores 

 of the infected tree, and, in every instance, insures a weak and 



