PLANTING, 11 



arranged in more regular order where they mark the concentric layers, and 

 the spaces between the rays are furnished with many cells irregularly 

 scattered over, of a size equal to those marking the concentric layers. 



The wood of the fir (o) is distinguished from all others here enumerated 

 by having very prominent coloured concentric layers, arranged very 

 regularly throughout ; and the cellular texture, though composed of cells 

 sufficiently large to be seen with the naked eye, is not to be distinguished 

 without very close observation. 



The lime (p) has very slender equal rays and a minute cellular texture 

 pervading the whole body of the wood. The concentric layers are 

 scarcely perceptible to the naked eye. It may be compared to the wood 

 of the poplar, but the network-like arrangement of the cellular texture is 

 not so obvious in the former ; the presence of the rays in the lime distin- 

 guishes it at once from the poplar. 



nnfe. 



The wood of the laburnum (9) is distinguished by its minute, regular, 

 uninterrupted medullary rays, and by the broken beaded longitudinal lines 

 of the tubular structure. 



These characters of distinction being permanent and constant in all these 

 different kinds of wood, will be found useful in cases where it is desirable 

 to ascertain the kind of timber which may have continued sound for the 

 longest period in any particular building or situation, arid the contrary 

 where its duration has been limited*. 



The leaves constitute one of the most important conservative organs of 

 vegetable growth ; for on the free and healthy exercise of their functions 

 depend the life of the plant and its progress to maturity, to say nothing of 

 that universal interest and pleasure which is afforded by the diversified 

 beauty of their forms and tints. The green colour of the leaves of trees 

 has been proved, beyond all doubt, to depend chiefly on the influence of 

 solar light and atmospheric air. Almost every distinct species and variety 

 of plant, in its most healthy state, has its own peculiar shade of green : 

 the yellow-green tint of the foliage of a healthy larch, would in that of a 

 pine, spruce, fir, and cedar of Lebanon, be certain indications of disease 

 and decay. The dissection of a leaf shews that it is composed of vessels, 

 cellular tissue, and an epidermis. The green part of a leaf is, in fact, a 

 continuation of the parenchyma of the bark before mentioned ; and the mid- 

 rib and nerves of the leaf are a continuation of the conducting and returning 

 sap, and air vessels of the bark and alburnum. The under and upper 

 surfaces of the leaf may be separated in an entire state from each other. 

 These appear to perform different offices ; the under surface is provided 



* It would be of the greatest utility to the interests of planting were registers kept 

 of the kinds of timber used in particular buildings ; also the age of the tree which pro- 

 duced it, when felled, and the soil, and situation or climate, in which the trees were 

 reared. Posterity would be grateful for such records of facts, 



