64 USES OF THE 



such European ones as are particularly related to 

 them, are distinguished for assuming various rich tints 

 in their foliage of red, yellow, white, or even blue, at 

 the decline of the year, witness the Guelder-rose, the 

 Cornel, the Vine, the Sumach, the Azalea pontlca, 

 Curt, Mag. i^. 433, and others. Fruits for the most 

 part incline to a red colour, apparendy from the acid 

 they contain. I have been assured by a first-rate 

 chemist that the colouring principle of the Raspberry 

 is a fine blue, turned red by the acid in the fruit. The 

 juices of some Fungi, as Boletus hovinus and Agaii- 

 cus cklk'iosus, Soxverb. Fuugi^ t. 202, change almost 

 instantaneously on exposure to the air, from yellow to 

 dark blue or green. 



These are a few hints only on a subject which opens 

 a wide field of inquiry, and which, in professedly che- 

 mical works, is carried to a greater length than I have 

 thought necessary in a physiological one. See Thorn- 

 sons Chem'istrif, v. 4. and JVilldenozvs Principles of 

 Botanij, 229. We must ever keep in mind, as we ex- 

 plore it, that our anatomical instruments are not more 

 inadequate to dissect the organs of a scarcely distin- 

 guishable insect, than our experiments are to inves- 

 tigate the fine chemistry of Nature, over which the 

 living principle presides. 



Before we take leave of the secreted fluids of ve^e- 

 tables, a few more remarks upon their direct utility to 

 the plants themselves may not be superfluous. Mal- 

 pighi first suggested that these secretions might nou- 



