VEGETABLE SAP. 115 



before asserted, is perfectly notorious. To no pur- 

 pose do we analyse the soil in which it grows, or the 

 water with which it has heen nourished, to detect the 

 qualities which are found in the root, stem, or leaves, 

 much less in the fruit. It must be remembered, that 

 in the areolated structure of vegetables all the appa- 

 ratus of the chemist's laboratory are found : alembics, 

 retorts, and all the natural machinery for absorp- 

 tion, nitration, condensation, and assimilation of 

 aqueous, vaporous, and gaseous bodies of the earth 

 and air, are silently and constantly in operation, and 

 the results are the production of the essential qualities 

 of the plant. 



In all the living members of a tree, as in the 

 seat of life, the recently formed layers of liber and 

 alburnum, the sap is capable of motion ; but in those 

 members which have already performed their func- 

 tions, and acquired form, namely, the outer bark, and 

 first formed layers of wood, it becomes concreted and 

 stationary. While capable of motion it usually ascends, 

 is transpirable, and consequently exhaustible. In the 

 latter case, the leaves and tender shoots become 

 flaccid and shrink; but when the exhausting cause 

 is withdrawn, or a sufficient supply of water is re- 

 ceived by the root, the shoots ^nd leaves quickly 

 regain their rigidity and vigour. This single incident 

 is a convincing proof of the ascent of the sap ; nothing 

 indeed can be more manifest. 



That the repletion of the sap vessels is kept up by 

 the agency of the roots and other absorbing organs of 



