the carbon dioxid 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.
