Imágenes de páginas
PDF
EPUB

The grape crop of the world is commercially valuable, because of the raisins and wine produced. Lemons, oranges, and grapefruit have come in recent years to give a living to many people in this country as well as in other parts of the world. The unfortunate city of Messina was the center of the lemon industry for Italy. Figs, olives, and dates are staple foods in the Mediterranean countries and are sources of wealth to the people there, as are coconuts, bananas, and many other fruits in tropical countries.

Beverages and Condiments. The coffee and cocoa beans, both products of tropical regions, form the basis of two very important beverages of civilized man. Pepper, black and red, mustard, allspice, nutmegs, cloves, and vanilla are all products manufactured from various fruits or seeds of tropical plants.

REFERENCE BOOKS

ELEMENTARY

Sharpe, A Laboratory Manual for the Solution of Problems in Biology. American Book Company.

Atkinson, First Studies of Plant Life, Chap. XXIII. Ginn and Company.

Bailey, Botany, Chaps. XXI, XXII. The Macmillan Company.

Bailey, Lessons with Plants, pages 251-314.
Beal, Seed Dispersal. Ginn and Company.

The Macmillan Company.

Bergen and Davis, Principles of Botany, Chaps. XL, XLI. Ginn and Company. Coulter, Plant Studies, Chap. VI. D. Appleton and Company.

Dana, Plants and their Children, pages 27-49. American Book Company.

Gannett, Garrison, and Houston, Commercial Geography. American Book Company.
Goff and Mayne, First Principles of Agriculture. American Book Company.

Lubbock, Flowers, Fruits, and Leaves. The Macmillan Company.
Newell, Reader in Botany, pages 97-137. Ginn and Company.

ADVANCED

Bailey, The Evolution of our Native Fruits. The Macmillan Company.

Bailey, Plant Breeding. The Macmillan Company.

Coulter, Barnes, and Cowles, A Textbook of Botany, Vol. I. American Book Com

pany.

De Candolle, Origin of Cultivated Plants. D. Appleton and Company.

Farmers' Bulletins, Nos. 78, 86, 225, 344. U.S. Department of Agriculture.

Hodge, Nature Study and Life, Chaps. X, XI. Ginn and Company.

Kerner (translated by Oliver), Natural History of Plants. Henry Holt and Company. 4 vols. Vol. II, Part 2.

Sargent, Corn Plants.

Houghton, Mifflin, and Company.

VI. SEEDS AND SEEDLINGS

Problem X. A study of seeds in their relation to the new plant. (Laboratory Manual, Prob. X.)

(a) The relation of the young plant to its food supply. (b) How the young plant makes use of its food supply.

[ocr errors]

Relation of Flower to Fruit. We have already found in our study of the fruit that the bean pod is a direct outgrowth from the flower. It is, in fact, the ovary of the flower, with the parts immediately surrounding it, which has grown larger to make a fruit.

[ocr errors]

Use of Fruit. The fruit holds and protects the seeds until the time comes when they are able to germinate and produce new

plants like the original plant from which they grew. Then, as we have seen, it helps to scatter them far and wide.

The Bean Seed.

[graphic]
[ocr errors]

-We have

already been able to identify in the pod of the bean the style, stigma, and ovary of the flower. The opened pod discloses the seeds lying along one edge of the pod, each attached by a little stalk to the inner wall of the ovary. If we pull a single bean from its attachment, we find that the stalk leaves a scar on the coat of the bean; this scar is called the hilum. The tiny hole near the hilum is called the micropyle. Turn

Three views of a kidney bean, the lower one having one cotyledon removed to show the hypocotyl and plumule.

back to the Figure (p. 37) showing the ovule in the ovary. Find there the little hole through which the pollen tube reached the embryo sac. This hole is called the micropyle, and is identical

[blocks in formation]

with the micropyle in the seed. The thick outer coat (the testa) is easily removed from a soaked bean, the delicate coat under it easily escaping notice. The seed separates into two parts; these are called the cotyledons. If you pull apart the cotyledons very carefully, you find certain other structures between them. The rodlike part is called the hypocotyl (meaning under the cotyledons). This will later form the root (and part of the stem) of the young bean plant. The first true leaves, very tiny structures, are folded together between the cotyledons. That part of the plant above the cotyledons is known as the plumule or epicotyl (meaning above the cotyledons). All the parts of the seed within the seed coats together form the embryo or young plant. A bean seed contains, then, a tiny plant tucked away between the cotyledons and protected by a tough coat.

Food in the Cotyledons. The problem now before us is to find out how the embryo of the bean is adapted to grow into an adult plant. Up to this stage of its existence it has had the advantage of food and protection from the parent plant. Now it must begin the battle of life alone. We shall find in all our work with plants and animals that the problem of food supply is always the most important problem to be solved by the growing organism. Let us see if the embryo is able to get a start in life (which many animals get in the egg) from food provided for it within its own body.

Test for Starch. If we shake up a piece of laundry starch in water, in a test tube, and then add to the mixture two or three drops of iodine solution, we find that the particles of starch in the test tube turn purple or deep blue. It has been discovered by experiment that starch, and no other known Starch grains in the cells substance, will be turned purple or dark blue. Therefore, iodine solution has come to be used as a test for the presence of starch. Starch in the Bean.-If we mash up a little piece of a bean cotyle

[graphic]

of a potato tuber.

1 Iodine solution is made by simply adding a few crystals of the element iodine to 95 per cent alcohol; or, better, take by weight 1 gram of iodine crystals, gram of iodide of potassium, and dilute to a dark brown color in weak alcohol (35 per cent) or distilled water.

don which has been previously soaked in water, and test for starch with iodine solution, the characteristic blue-black color appears, showing the presence of the starch. If a little of the stained material is mounted in water on a glass slide under the compound microscope, you will find that the starch is contained in the form of little ovoid bodies called starch grains. The starch grains and other food products are made use of by the growing plant.

Starches and sugars make up the great class of nutrients known as carbohydrates. Of these we shall learn more when we take up the study of foods. (The teacher may here refer to the chapter on Foods.)

Proteid in the Bean. Another nutrient present in the bean cotyledon is proteid. Several tests are used to detect the presence of this nutrient. The following is one of the best known:

Place in a test tube the substance to be tested; for example, a bit of hard-boiled egg. Pour over it a little strong (80 per cent) nitric acid. Note the color that appears a lemon yellow. If the egg is washed in water and a little ammonium hydrate added, the color changes to a deep orange, showing that a proteid is present.

If the proteid is in a liquid state, its presence may be proved by heating, for when it coagulates or thickens, as does the white of an egg when boiled, proteid in the form of an albumin is present.

Another characteristic proteid test easily made at home is burning the substance. If it burns with the odor of burning feathers or leather, then proteid forms part of its composition.

Proteids occur in several different forms, but the preceding tests will cover most cases commonly met. White of egg, lean meat, beans, and peas are examples of substances composed in a large part of proteid.

A test of the cotyledon of a bean for proteid food with nitric acid and ammonium hydrate shows us that considerable proteid is present. It contains not less than 23 per cent of proteid, 57 per cent of carbohydrates, and about 2 per cent of fats.

The above tests show us that the bean seed contains a large supply of food which, as we shall see, is used by the young plant in its germination.

Beans and Peas as Food for Man. The young plant within a pea or bean is well supplied with nourishment until it is able to take care of itself. In this respect it is somewhat like a young animal within the egg, a bird or fish, for example. So much food is stored in legumes (as beans and peas are named) that man has come to consider them a very valuable and cheap source of food. The following table shows the amount of food material that can be purchased for 10 cents in fresh and dried peas and beans.

NUTRIENTS FURNISHED FOR TEN CENTS IN BEANS AND PEAS AT CERTAIN PRICES PER POUND

[merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][subsumed][merged small][merged small][subsumed][merged small][merged small][subsumed][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small]

The Corn. The ear of corn is not a single fruit, but a large number of fruits in a cluster like a bunch of bananas, for example. The husk of an ear of corn is simply a covering of leaflike parts which has grown over the young fruits for their better protection. The corn cob is the much thickened flower stalk on which the flowers were clustered. If you have removed the husk carefully, you will see part of each flower remaining attached to each grain of corn. The so-called silk of corn is nothing more than a long style and stigma. The corn grain itself was also part of the

« AnteriorContinuar »