3. Animals require water, mineral matter, protein, sugar, starch, and fat.
4. Plants require the same; but the seed being a storehouse part of the plant, it will not have sugar, and water has to be supplied when the new plant is to be formed.
5. Seeds contain, therefore, mineral matter, protein, starch, and fat.
Note 1.—Seeds will grow in water until their stored food is used: they must then be planted in soil, to get further nourishment.
Note 2.—The two fuel foods, starch and fat, are not found together in abundance in seeds; one or the other will be much in excess. For instance, in walnuts there is a great deal of fat, while in peas and beans there is scarcely a trace of fat, but the starch is abundant.
COMPARATIVE FOOD VALUE OF DIFFERENT PARTS OF PLANTS
Only a very general idea of this should be attempted. The food value of any part of a plant can be roughly estimated by considering the office of that particular part in plant structure. Nature study will assist in this. The root collects the food to send it to the parts above; the stem is a hallway through which the food is carried in a more diluted form. The leaves serve the purpose of lungs and will not contain much food, though they naturally have a good deal of flavour; parsley, sage, and tea are examples of this. The fruit is a house to protect the seeds, and is made most attractive and delicious, so that animals will be tempted to eat this part, and thus assist in the dispersal of the seeds. The fruit has comparatively little food value as building material. The seed contains the stored material to build new plants, and therefore is the most nutritive part of all. It is the only part of the plant which contains an appreciable supply of building food, that is, which can take the place of eggs or meat in the diet. Baked beans are sometimes called "nuggets of nourishment" or "the poor man's beef".
Lesson IV
After discussing the food value of the different parts in this broad way, the pupils may be asked to consider the plant foods used in their diet and to compare their nutritive value.
The facts concerning these may be summed up as follows: