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In adverting to lieat as essential to vegetation, it is par- 

 ticularly worthy of notice, as already observed, that the epi- 

 dermis and bark of trees, drawn up by shelter, are usually 

 thin, the fornier often smooth and glossy. The descending 

 vessels, by consequence, as they lie under it, never fail to 

 suffer severely, on being exposed to a cold atmosphere. It 

 is greatly on this account, as well as from scantiness of roots 

 and lateral boughs, that plantations sustain such extensive 

 injury, on being suddenly thinned. Where that operation 

 is performed in a gradual manner, it gives time for nature 

 to prepare the trees for the change, by strengthening the 

 coat of bark, and likewise by multiplying the roots, and 

 thickening the spray and branches ; and thus the proper 

 vessels are prevented from being chilled by untimely expo- 

 sure. The fact, though universally known, is never referred 

 to the true cause, by common observers. 



These considerations furnish ample ground to admire the 

 wise provision of nature, in bestowing a much thicker, 

 coarser, and more indurated covering of bark upon all trees 

 in open exposures : for in vain might they possess every 

 other property, if the sap-vessels were not sufficiently pro- 

 tected, and enabled to do their office. Were that to happen, 

 through the thinness of the bark, there cannot be a doubt, 

 but that the plants would become stunted and sickly, and 

 both branches and spray would suffer injury in consequence, 

 as we see happen to the generality of transplanted trees, 

 which do not possess this protecting property. From all 

 which it appears, that the health and protection of the proper 

 vessels, by means of a due thickness and induration of bark, 

 is an indispensable prerequisite in all subjects meant for 

 removal, and that it is deserving of the rank here assigned 

 to it. 



Secondly : Girth and Stoutness of Stem. Next to thick- 

 ness of bark, the fitness of the tree for removal greatly 

 depends on this property. The stem or trunk of woody 



