How to know the chief characters of some great animal groups.
Laboratory Suggestions
A visit to a botanical garden or laboratory demonstration.—Some of the forms of plant life. Review of essential facts in development of bean or corn embryo.
Demonstration.—Charts or models showing the development of a many-celled animal from egg through gastrula stage.
Demonstration.—Types which illustrate increasing complexity of body form and division of labor.
Museum trip.—To afford pupil a means of identification of examples of principal phyla. This should be preceded by objective demonstration work in school laboratory.
Reproduction in Plants.—Although there are very many plants and animals so small and so simple as to be composed of but a single cell, by far the greater part of the animal and plant world is made up of individuals which are collections of cells living together.
A cell of pond scum. How might it divide to form a long thread made up of cells?
In a simple plant like the pond scum, a string or filament of cells is formed by a single cell dividing crosswise, the two cells formed each dividing into two more. Eventually a long thread of cells is thus formed. At times, however, a cell is formed by the union of two cells, one from each of two adjoining filaments of the plant. At length a hard coat forms around this cell, which has now become a spore. The tough covering protects it from unfavorable changes in the surroundings. Later, when conditions become favorable for its germination, the spore may form a new filament of pond scum. In molds, in yeasts, and in the bacteria we also found spores could be formed by the protoplasm of the plant cutting up into a number of tiny spores. These spores are called asexual (without sex) because they are not formed by the union of two cells, and may give rise to other tiny plants like themselves. Still other plants, mosses and ferns, give rise to two kinds of spores, sexual and asexual. All of these collectively are called spore plants.