Ontario Teachers' Manuals: Nature Study

by Ontario. Department of Education

SEED DISPERSAL

The lessons on seed dispersal which were begun in Form I should be continued in this Form.

I. LESSON

Select a few weeds belonging to species which produce large numbers of seeds, such as wild mustard, white cockle, false-flax, etc. Distribute the seed pods among the pupils of the class and require them to estimate the number of seeds produced by each plant.

By references to observations made in the garden, help the pupils to recall the bad results, both to parent plants and to young seedlings, of improper scattering of seeds, namely:

1. The excessive crowding and shading, which causes the plants to become weak.

2. Insufficient food and moisture for the large number of plants, which causes the plants to be small and worthless.

Discuss how the crowding of cultivated plants is prevented and, in a general way, how nature provides for the scattering of seeds.

The great work of the plant is the production and dispersal of its seeds.

Ask the pupils to be on the alert to find examples of plants in which provision is made for the dispersal of the seeds, and to bring these plants to the class for the next lesson.

DETAILED STUDY OF SEED DISPERSAL

II. CLASS-ROOM LESSON

Make use of the specimens gathered by the pupils and by the teacher for observing and classifying as follows:

1. Seeds that steal rides. Examples—burdock, blue burr, pitch-fork weed, barley, stick-tight, hound's tongue.

2. Seeds that are carried in edible fruits which have attractive colours, tastes, etc. Examples—apple, grape, cherry, rowan, hawthorn.

3. Seeds that are carried by the wind. Examples—dandelion, thistle, milkweed, maple, pine, elm.

4. Seeds that are scattered by being shot from bursting pods. Examples—violet, jewel-weed (touch-me-not), sweet-pea, witch-hazel.

5. Seeds that are scattered by plants which are rolled along by the wind. Examples—Russian thistle, tumble-mustard, tumble-grass.

6. Seeds that float. Very many seeds float, although not specially fitted for floating, and some, such as the cocoa-nut and water-lily, are especially adapted for dispersal by water.

To the teacher.—Require the pupils to observe the special structure that facilitates the dispersal of the seed. As an illustration, ask the pupils to find the seeds of the burdock and to describe what the burr is really like. They find that the burr is a little basket filled with seeds. The basket has many little hooks which catch on the hair of animals and, since these hooks turn inwards, they serve to hold the basket in such a position that all the seeds are not likely to drop out at one time. The pupils should also observe that these baskets are quite firmly attached to the parent plant until the seeds are ripe; after that the baskets break off the plant at the slightest pull.

SEED COLLECTIONS

During late summer and in the autumn the seeds of the weeds that have been identified by the pupils should be collected.

Instruct the pupils to rub the ripened seed pods between the hands until the seeds are thrashed out, at the same time blowing away the chaff. The seeds are now placed in small phials or in small envelopes and these are carefully labelled. If possible, fill each phial so that there may be sufficient seed for use by all the members of the class in the lessons on seed description and identification which are to be taken during the winter months, when Nature Study material is less plentiful than it is in the summer and autumn. The phials or envelopes may be stored in a shallow box, or the phials may be mounted on a stout card. They may be attached to this card either by stout thread sewed through the card and passing around the phial, or by brass cleats, which may be obtained with the phials from dealers in Nature Study supplies.

MAN AS A DISPERSER OF SEEDS

Man as an agent in the dispersal of seeds should be made a topic for discussion.

Obtain, through the pupils, samples of seed-grain, clover seed, timothy seed, turnip seed, etc. Ask the pupils to examine these and count the number of weed seeds found in each.

The results will reveal a very common way in which the seeds of noxious weeds are introduced.

Describe the introduction from Europe to the wheat-fields of the Prairie Provinces of such weeds as Russian thistle, false-flax, French-weed. The seeds of these weeds were carried in seed-grain, fodder for animals, and also in the hay and straw used by the immigrants as packing for their household goods.

Careful farmers will not allow thrashing-machines, seed drills, fanning-mills, etc., to come from farms infested with noxious weeds to do work upon their farms, nor will they buy manure, straw, or hay that was produced on dirty farms.