Fig. 130.—An Apple Tree, with suggestions as to pruning when it is set in the orchard. At a is shown a pruned top.
111. Give some reasons why plants very close to a house may not thrive or may even die. 112. Why are fruit trees pruned or thinned out as in Fig. [129]? Proper balance between top and root. 113. We have learned that the leaf parts and the root parts work together. They may be said to balance each other in activities, the root supplying the top and the top supplying the root (how?). If half the roots were cut from a tree, we should expect to reduce the top also, particularly if the tree is being transplanted. How would you prune a tree or bush that is being transplanted? Fig. [130] may be suggestive.
CHAPTER XIV
DEPENDENT PLANTS
Thus far we have spoken of plants that have roots and foliage and that depend on themselves. They collect the raw materials and make them over into assimilable food. They are independent. Plants without green foliage cannot make food; they must have it made for them or they die. They are dependent. A sprout from a potato tuber in a dark cellar cannot collect and elaborate carbon dioxide. It lives on the food stored in the tuber.
Fig. 131.—A Mushroom, example of a saprophytic plant. This is the edible cultivated mushroom.
All plants with naturally white or blanched parts are dependent. Their leaves do not develop. They live on organic matter—that which has been made by a plant or elaborated by an animal. The dodder, Indian pipe, beech drop, coral root among flower-bearing plants, also mushrooms and other fungi (Figs. [131], [132]) are examples. The dodder is common in swales, being conspicuous late in the season from its thread-like yellow or orange stems spreading over the herbage of other plants. One kind attacks alfalfa and is a bad pest. The seeds germinate in the spring, but as soon as the twining stem attaches itself to another plant, the dodder dies away at the base and becomes wholly dependent. It produces flowers in clusters and seeds itself freely (Fig. [133]).
Fig. 132.—A Parasitic Fungus, magnified. The mycelium, or vegetative part, is shown by the dotted-shaded parts ramifying in the leaf tissue. The rounded haustoria projecting into the cells are also shown. The long fruiting parts of the fungus hang from the under surface of the leaf.