Page:An introduction to physiological and systematical botany (1st edition).djvu/113

 Rh sometimes propagated by seed, and are almost invariably permanent if the plants be propagated 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 Rumex, 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 Sumach, 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 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,