Page:The Olive Its Culture in Theory and Practice.djvu/151

Rh The black fungus is due solely to local causes. There is either too much dampness or not enough light. The infected branches should be cut off and burned and the tree sprayed with kerosene as heretofore described. No olive tree on ground high enough for a sufficiency of air and ventilation was ever afflicted with this pest. The cultivation of the soil provokes moisture and stimulates the vegetable growth of the tree, so where the black fungus appears, cease this cultivation, do not stir up the soil, but on the contrary check the excessive growth and humidity, by allowing the surface of the ground to harden. Prune the trees so that each may have a maximum of light and air. If the excess of moisture cannot be remedied by these means, the soil must be drained.

VISCIM ALBUM, MISTLETOE. The mistletoe is propagated from one tree to another by its seed. It extends its green roots through the branches from which it draws its nourishment, greatly enfeebling the tree. The only method of destroying it is, to cut off the branches on which it has effected a lodgment, and burn them.

LICHENS AND MOSSES. It is erroneously claimed by many writers that the mossy substance which grows upon the trunk and branches of the olive and other trees is a parasite. Instead it is composed of moss and lichens, the principal ones of which are Parmelia, Lecanara, Verrucaria, etc., among the lichens, and Hypsum, Leskea, Bryum and Orthotrichum among the mosses.

These last are cormus fungi, and all are epiphytes and live on the outside of the dead bark and exercise no parasitical influence. They shield the bark from the sun, but the humidity they engender is a frequent cause of rot, and they also serve as nesting places for hurtful insects. For these reasons it is well to liberate the trees from them by scraping the infected parts, or spraying with a solution of lime.