Pour in a little water. Observe the rise of the water due to the pressure from below (Fig. 128). Some plants yield a large amount of water under a pressure sufficient to raise a column several feet; others force out little, but under considerable pressure (less easily demonstrated). _The vital processes_ (_i.e._, the life processes). =100.= The pupil having studied roots, stems, and leaves, should now be able to describe the main vital functions of plants: what is the root function? stem function? leaf function? =101.= What is meant by the “sap”? =102.= Where and how does the plant secure its water? oxygen? carbon? hydrogen? nitrogen? sulfur? potassium? calcium? iron? phosphorus? =103.= Where is all the starch in the world made? What does a starch-factory establishment do? Where are the real starch factories? =104.= In what part of the twenty-four hours do plants grow most rapidly in length? When is food formed and stored most rapidly? =105.= Why does corn or cotton turn yellow in a long rainy spell? =106.= If stubble, corn stalks, or cotton stalks are burned in the field, is as much plant-food returned to the soil as when they are plowed under? =107.= What process of plants is roughly analogous to perspiration of animals? =108.= What part of the organic world uses raw mineral for food? =109.= Why is earth banked over celery to blanch it? =110.= Is the amount of water transpired equal to the amount absorbed? =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. [Illustration: FIG. 126.--TO ILLUSTRATE TRANSPIRATION.] [Illustration: FIG. 127.--LOSS OF WATER.] [Illustration: FIG. 128.--TO SHOW SAP PRESSURE.] [Illustration: FIG. 129.--BEFORE AND AFTER PRUNING.] [Illustration: FIG. 130.--AN APPLE TREE, with suggestions as to pruning when it is set in the orchard. At _a_ is shown a pruned top.] CHAPTER XIV DEPENDENT PLANTS Thus far we have spoken of plants with 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 dioxid. It lives on the food stored in the tuber.