COLOURS OF PLANTS. 83 



sometimes propagated by seed, and are al- 

 most invariably permanent if the plants be pro- 

 pagated by roots, cuttings or grafting. Plants 

 of an acid or astringent nature often become 

 very red in their foliage by the action of light, 

 as in Humeri Polygonum, Epilobium and 

 Berberis ; and it is remarkable that American 

 plants in general, as well as 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 Su- 

 mach, the Azalea pontica, Curt Mag. t. 433, 

 and others. Fruits for the most part 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 Agaricus deliciosus, 

 Sowerb. Fungi, t. 202, change almost instan- 

 taneously 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, 



g2 



