COLOURS OF PLANTS. 83 



sometimes propagated by seed, and are al- 

 most invariably permanent if tlie plants be pro- 

 pagated by roots, cuttings or grafting. Plants 

 of an acid or astringent nature often become 

 very red in their foliatre by the action of lio-ht, 

 as in RumcT, Foli/gomnn, Epilohium 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 fn-st-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 bovlnus and Agarkus 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, 



G 2 



