(2) Of gra.s.ses (cereals)--wheat, corn, rice
(3) Of vines (legumes)--peas, beans, lentils.
In asking for examples of the different parts, there will be more interest and value if the questions correlate other subjects, for instance: For what fruit is Canada noted? What fruit does she import?
Name a nut the squirrels gather.
LESSON II
COMPOSITION OF ANY PART OF A PLANT
From the foregoing, the pupils may infer that there are eight different foods to study. They should be led to see that in reality there is only one, as all parts of plants are, generally speaking, the same in structure. Referring to the animal body, they will know that a bone from the foot is of much the same structure as one from the face; that a piece of flesh from the leg is the same as a piece from any other part of the body. In the same way, if we study one part of a plant, it will be a type of all parts. In general the structure is as follows:
1. A framework, in cellular form, made of a substance called _cellulose_.
2. Material filling the cells:
(1) A juice in the cells of all parts of plants except seeds
(2) A solid in the cells of seeds.
To show the framework, some vegetable food having a white colour should be chosen, such as potato, parsnip, or apple.
It must be explained that all plants are made of a framework of numerous cells, something like a honey-comb. The cells in plants are of many different shapes, according to the plant, or the part of the plant, in which they are found. They are usually so small that they cannot be distinguished without a microscope; but occasionally they are large enough to be seen without one. Pa.s.s sections of orange or lemon, where the cells are visible. Make a drawing on the black-board of the cellular formation of a potato. Lead the cla.s.s to understand that, in every case, the cell walls must be broken to get out the cell contents. To ill.u.s.trate this, they may use potatoes, and break the cell walls by grating the potatoes. After they have broken up the framework, the cell contents should be strained through cheesecloth into a gla.s.s. They have now two parts to examine--cell walls and cell contents.
[Ill.u.s.tration: Cellular structure of a potato]
Wash the framework to free it of any cell juice and study it first. Give its name, and note its colour and texture. Compare the framework of potatoes, strawberries, lettuce, trees, etc. Tell the cla.s.s that in some cases part of the cellulose is so fibrous that it is used to make thread, cloth, or twine; for instance, _flax_ and _hemp_.
Cellulose is most difficult to dissolve, so that practically little of it is digested. It serves a mechanical purpose in the digestive tract by helping to fill the organs and dilute the real food. If fibrous, it acts as an irritant and overcomes sluggishness of the intestines known as constipation. The outer coats of cereals are an example of coa.r.s.e cellulose, as used in brown bread and some kinds of porridge.
Examine next the juice which was contained in the cells of the potato.
The liquid shows much water; the colour indicates mineral matter in solution; the odour suggests a flavour; the white sediment is starch.
COMPOSITION OF POTATO JUICE
Water, mineral matter, flavouring matter, starch.
Draw attention to the fact that the potato is the part of the plant which acts as a storehouse. In such parts, starch is always found as the stored form of sugar; but, in parts which are not storehouses, sugar will be found in its stead. In rare cases both are found, as in the parsnip.
NOTE.--This is a good time to impress the fact that plants are the source of starch for manufacturing purposes. In England, potatoes are largely used; in Canada, corn. It will be interesting to state that the early settlers obtained their starch for laundry purposes at home from potatoes, by chopping or grinding them.
The insolubility of starch in cold liquids may be effectively reviewed at this part of the lesson. The starch has been lying in the water of the potato cells for several months, yet has not dissolved. Let two or three of the cla.s.s gradually heat the potato juice with its starch sediment, stirring all the time to distribute the sediment evenly. They will find that a little less than boiling temperature dissolves the starch. This will show them that heat is necessary for the solution of starch, and a heat much greater than that in the body, hence raw starch is indigestible. Recall the milk lesson and the uselessness of starch as a component of milk, unless the milk be cooked.
Squeeze the juice from a sour apple or lemon, and note the taste.
Explain that all fruit juices contain more or less acid. The effects of this acid in the body are similar to those of mineral matter.
Protein is also found in plant juices; but in such small quant.i.ties that it may be disregarded as a source of food supply.
GENERAL COMPOSITION OF PLANT JUICE
Water; mineral matter; flavouring matter; starch or sugar, or both; acid (in fruit juice).
LESSON III
COMPOSITION OF SOLID MATERIAL IN CELLS OF SEEDS
This part of the lesson may be developed as follows:
1. Seeds contain the building material for new plants, as well as their food for a short time.
2. Plants and animals require much the same material to build and feed them.
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 a.s.sist 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 a.s.sist 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:
1. Green vegetables:
These generally contain much water, hardly any protein or fat, and a small amount of sugar.
They are valuable mainly for their mineral matter and cellulose.
2. Root vegetables and tubers:
These are more nutritious than green vegetables, because they contain much more sugar and starch.