XIV. DIVISION OF LABOR. THE VARIOUS FORMS OF PLANTS AND ANIMALS _Problems.--The development and forms of plants._ _The development of a simple animal._ _What is division of labor? In what does it result?_ _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. [Illustration: 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_. [Illustration: The formation of spores in pond scum. _zs_, zygospore; _f_, fusion in progress.] Reproduction in Seed Plants.--Another great group of plants we have studied, plants of varied shapes and sizes, produce seeds. They bear flowers and fruits. [Illustration: The formation and growth of a plant embryo. 1, the sperm and egg cell uniting; 2, a fertilized egg; 3, two cells formed by division; 4, four cells formed from two; 5, a many-celled embryo; 6, young plant; _H_, hypocotyl; _P_, plumule; _C_, cotyledons.]