LECT. III.] THE SAP. 107 



less progress vegetation has made, it is obtained 

 in a purer state. It should, therefore, be drawn 

 very early in the spring, before the leaves expand, 

 and as near to the root of the plant as it can easily 

 be obtained, if we wish to examine its chemical 

 properties. 



When the sap is thus drawn from a tree, it 

 usually appears nearly as colourless and limpid 

 as water, has scarcely any taste and no particular 

 odour. A phial containing a certain quantity of 

 sap weighs heavier than the same phial, contain- 

 ing an equal portion of distilled water ; so that the 

 specific gravity of sap is greater than that of 

 water. If it be kept for some time in a warm 

 place, it undergoes sometimes the acetous, at 

 other times the vinous, and in some instances even 

 the putrefactive fermentation. These differences 

 would indicate a great disparity in the compo- 

 nents of the sap of different vegetables ; but there 

 is every reason for thinking that they depend more 

 on the admixture of the proper juices, which, as I 

 have already stated, are always more or less mixed 

 with the sap, as we can obtain it ; and it is probable, 

 that the sap of different plants differs more in the 

 proportional quantity of these juices mixed with it, 

 than in the nature of its components. The rapid 

 vinous fermentation of some kinds of sap is taken 

 advantage of in warm climates for economical 

 purposed. From the top of the Cocoa-nut tree 



