Saprophytes break down or decompose organic substances. Chief of these saprophytes are many microscopic organisms known as bacteria (Fig. [135]). These innumerable organisms are immersed in water or in dead animals and plants, and in all manner of moist organic products. By breaking down organic combinations, they produce decay. Largely through their agency, and that of many true but microscopic fungi, all things pass into soil and gas. Thus are the bodies of plants and animals removed and the continuing round of life is maintained.
Fig. 136.—American Mistletoe Growing on a Walnut Branch.
Some parasites are green-leaved. Such is the mistletoe (Fig. [136]). They anchor themselves on the host and absorb its juices, but they also appropriate and use the carbon dioxide of the air. In some small groups of bacteria a process of organic synthesis has been shown to take place.
Epiphytes.—To be distinguished from the dependent plants are those that grow on other plants without taking food from them. These are green-leaved plants whose roots burrow in the bark of the host plant and perhaps derive some food from it, but which subsist chiefly on materials that they secure from air dust, rain water, and the air. These plants are epiphytes (meaning “upon plants”) or air-plants.
Epiphytes abound in the tropics. Certain orchids are among the best known examples (Fig. [37]). The Spanish moss or tillandsia of the South is another. Mosses and lichens that grow on trees and fences may also be called epiphytes. In the struggle for existence, the plants probably have been driven to these special places in which to find opportunity to grow. Plants grow where they must, not where they will.
Suggestions.—114. Is a puffball a plant? Why do you think so? 115. Are mushrooms ever cultivated, and where and how? 116. In what locations are mushrooms and toadstools usually found? (There is really no distinction between mushrooms and toadstools. They are all mushrooms.) 117. What kinds of mildew, blight, and rust do you know? 118. How do farmers overcome potato blight? Apple scab? Or any other fungous “plant disease”? 119. How do these things injure plants? 120. What is a plant disease? 121. The pupil should know that every spot or injury on a leaf or stem is caused by something,—as an insect, a fungus, wind, hail, drought, or other agency. How many uninjured or perfect leaves are there on the plant growing nearest the schoolhouse steps? 122. Give formula for Bordeaux mixture and tell how and for what it is used.
CHAPTER XV.
WINTER AND DORMANT BUDS
A bud is a growing point, terminating an axis either long or short, or being the starting point of an axis. All branches spring from buds. In the growing season the bud is active; later in the season it ceases to increase the axis in length, and as winter approaches the growing point becomes more or less thickened and covered by protecting scales, in preparation for the long resting season. This resting, dormant, or winter body is what is commonly spoken of as a “bud.” A winter bud may be defined as an inactive covered growing point, waiting for spring.
