CH. III.] THE STEM AND BRANCHES. J 31 



terstices of which are filled up with soluble matter, 

 differing in each vegetable genus, but closely resem- 

 bling its parenchj-ma The layer immediately in 

 contact with the bark is the softest and palest in 

 colour, and thence is called the alburnum. It is in 

 this that the vessels which convey the sap from the 

 roots to the leaves are chiefly situated. This layer is 

 annually renewed, that of the previous year becoming 

 more complete wood. Although the chief part of the 

 sap vessels, as just observed, is situated in the albur- 

 num, yet others, though more scantily, are dispersed 

 through the whole of the w^ood. Wherever situated, 

 they extend from the extremity of the minutest root 

 to the leaves. The idea that the annular layer of 

 wood is rendered more dense and firm by severe 

 winters, is denied by reason, and demonstrated to be 

 false by actual obsei-vation. The layers are thickest 

 on those sides of a tree where the largest branches 

 occur, and are, throughout, of greater size, in such 

 years as afford the most genial period to vegetation. 

 Wood is consolidated fastest m those plants which 

 are most freely exposed to the influence of light and 

 air, and those plants grow in height the slowest. 

 This teaches a lesson to the gardener he often may 

 remember with advantage ; for it is often desirable 

 to have specimens of the same shrub, varying in 

 height ; and he may often increase their stature, yet 

 preserve them in health, by keeping them in a moist, 



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