116 PHYSIOLOGY OF VEGETABLES. 



Observation. 1. When the cambium first begins to be fibrous, 

 although produced by the bark, yet it adheres so much more 

 firmly to the wood, that it remains* quite entire upon it when the 

 bark is removed. It contains much saccharine matter, and in 

 those trees, in which it is not tinctured with any disagreeable 

 property of the plant, as bitterness, it is palatable. 



It is particularly so in the Birch. Children, in the country, 

 sometimes seek for it, and appear to be as fond of it as they are 

 of fruit. 



2. At the season when the cSnbium is perfectly formed, trees 

 maybe stripped of their bark entirely without injury, a new bark 

 being speedily formed upon them. This has been thought to 

 prove, that the wood had power to produce anew bark I have sev- 

 eral times made the experiment on forest trees with perfect suc- 

 cess, and from some circumstances attending it, am inclined to 

 the following opinion. That the cambium, containing the rudi- 

 ment of a new layer of bark, as well as of a new layer of 

 wood, is not removed with the bark, but remains undisturbed on 

 the trunk, and thus the new bark, which forms in this case, is not 

 formed by the wood, but had its rudiment previously formed by 

 the bark. This method of removing the old bark has been turned 

 to advantage in fruit trees, whose bark had become bound. Care 

 should be taken not to injure the pulp of the cambium. It should 

 be protected from the weather a while b} some soft covering. 



In animals, the trunks of the arteries serve as mere 

 channels to convey the blood into the extreme vessels, 

 which are distributed throughout e/ery fibre of the 

 body. It is in these extreme vessels, that the great 

 vital functions go on ; in these it is, that parts are in- 

 creased or renewed, and in these animal heat is pro- 

 duced. The veins collect the blood, after it has^erform- 

 ed these function.^ and return it through the medium of 

 the heart, to the lungs, to be renewed by the air, and 

 sent round again by the arteries. 



In the vegetable, the sap-vessels are analogous to 

 the veins, and .the vessels of the leaf to the extreme 

 vessels of the lungs. The vessels of the bark, are com- 

 pared to the arteries. There are not any vessels in 

 vegetables, which carry the descending sap back 

 again from the bark to the vessels of the sap-wood 

 to be recirculated. The sap is supposed to be exhaust- 

 ed altogether, by nourishing the plant in its descent. 



