SECRETION. 97 



processes hitherto described, an elaboration of matter 

 useful for the further support of it, and a separation of 

 matter which is not so, but may be separated from it, 

 both take place ; but it is often difficult to say what is 

 so useful, or what is detrimental, and may more or less 

 be dispensed with. 



99. After the crude sap has passed through the 

 leaves and becomes altered by the process of digestion 

 there taking place, it descends through the bark, in 

 which it is found very materially different in nature and 

 property, but varying according to the plant in which it 

 is examined. 



100. This fluid, to which the term Proper Juice is 

 most correctly applied, contains different products, which 

 are afterwards to be seen as excretions from the plant, 

 though at one time many of them, along with the fluid 

 they are contained in, serve as nourishment to it, and 

 go to the formation of its several organs. 



101. The proper juice, along with its contained pro- 

 ducts, is here looked upon for convenience of descrip- 

 tion as a secretion, though the main portion of it per- 

 haps is at once derived as an assimilated fluid from the 

 leaves after digestion, in which the objects to be se- 

 creted are formed after a time. 



102. According to the nature of these objects which 

 predominate, and therefore give a character to the fluid 

 in which they are found, proper juices may be divided 

 into three classes : 



1. Resinous and gummy juices. 



2. Caoutchouc juices. 



3. Albuminous juices. 



103. The proper juices of most plants have resin or 

 gum as then: chief ingredient : in some it is almost 

 impossible to say which predominates. The Poppy has 

 a juice belonging to this division, at least according to 

 the analysis of Bucholz ; and here are to be placed the 

 juices of the milky Euphorbias, and of the trees yielding 

 Gamboge, etc. 



