COLOURS OF PLANTS, 



-79 



are sometimes propagated by seed, and are almost inva- 

 riably permanent if the plants be propagated by roots, 

 cuttings or grafting. Px mts of an acid or astringent 

 nature often become very red in their foliage by the ac 

 tionoflight, asini?^.72^a:, Polygonum, Epilobhim zndi 

 Berheris ; and it is remarkable that American plants 

 in general, as well as such European ones as are par- 

 ticularly 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 pontica. Curt. Mag. t. 433, and others. Fruits 

 for the most p^rt incline to a red colour, apparently 

 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 bovinus 

 and Agarlcus deliciosus, Sowerb. Fungi, t, 202, change 

 almost instantaneously on exposure to\he air, from vgI 

 low 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 chem- 

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

 thought necessary in a physiological one. See T/zom- 

 •son^s Chemistrt/, v. 4, and midenow^s Principles of 

 Botany, 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 experimems are to investigate 

 the fine chemistry of Nature, over which the living pin, 

 ciple presides . 



