CHAP. III. FUNCTION OF NUTRITION. 215 



Some are the results of disease, whilst others are more 

 abundantly formed when the plants which produce 

 them are placed in peculiar soils and situations. Some 

 occur in a very few species only, whilst others are 

 characteristic of whole families. None of them are 

 so abundantly diffused as the four nutritive sub- 

 stances already described ; and they all materially 

 differ from these, by having either the oxygen or the 

 hydrogen which they contain in greater excess than 

 would be necessary to form water. These may there- 

 fore be termed hyperoxygenated and hyperhydrogen- 

 ated products, when contrasted with the others. 

 Little is at present known of the exact manner in 

 which these various products are formed. Their com- 

 plete enumeration belongs to the department of che- 

 mical Botany ; and we can here pretend to do no 

 more than point out some of the principal groups, and 

 mention a few of their most striking peculiarities. 



(202.) Proper Juices. Several of the products 

 elaborated in the leaves and cortical parts, are dissolved 

 in those proper juices of plants which in art. 1.Q5. 

 we described as the latex or vital fluid, analogous to 

 the blood of animals. But as these juices are very 

 different in their characters in different species, as they 

 are not clearly defined in some and above all as they 

 act as poisons when imbibed by the roots, De Candolle 

 imagines that they ought more properly to be con- 

 sidered as secretions of a recrementitial nature, ana- 

 logous to the bile and others in the animal economy. 

 Some of these products even contain azote, and by 

 this circumstance are brought into closer resemblance 

 with animal matter. The more remarkable materials 

 found in the proper juices of plants are milks, resins, 

 and oils. 



(203.) Milks These are generally of an opaque 



white, though some are variously coloured. They 

 abound in many species, and are highly characteris- 

 tic of certain natural families, as the Euphorbiaceae, 

 p 4 



