The Life Cycle.--Ultimately both plants and animals grow old and die. Some plants, for example the pea or bean, live but a season; others, such as the big trees of California, live for hundreds of years. Some insects exist as adults but a day, while the elephant is said to live almost two hundred years. The span of life from the time the plant or animal begins to grow until it dies is known as the _life cycle_. REFERENCE BOOKS ELEMENTARY Hunter, _Laboratory Problems in Civic Biology_. American Book Company. Andrews, _A Practical Course in Botany_, pages 112-127. American Book Company. Atkinson, _First Studies of Plant Life_, Chaps. IV, V, VI, VIII, XXI. Ginn. Coulter, _Plant Life and Plant Uses_, Chap. V. American Book Company. Dana, _Plants and their Children_, pages 99-129. American Book Company. Mayne and Hatch, _High School Agriculture_. American Book Company. Hodge, _Nature Study and Life_, Chaps. IX, X, XI. Ginn and Company. MacDougal, _The Nature and Work of Plants_. The Macmillan Company. ADVANCED Apgar, _Trees of the United States_, Chaps. II, V, VI. American Book Company. Coulter, Barnes, and Cowles, _A Textbook of Botany_, Vol. I. American Book Company. Duggar, _Plant Physiology_. The Macmillan Company. Ganong, _The Teaching Botanist_. The Macmillan Company. Goebel, _Organography of Plants_, Part V. Clarendon Press. Goodale, _Physiological Botany_. American Book Company. Gray, _Structural Botany_, Chap. V. American Book Company. Kerner-Oliver, _Natural History of Plants_. Henry Holt and Company. Strasburger, Noll, Schenck, and Karston, _A Textbook of Botany_. The Macmillan Company. Ward, _The Oak_. D. Appleton and Company. Yearbook, U. S. Department of Agriculture, 1894, 1895, 1898-1910. IX. OUR FORESTS, THEIR USES AND THE NECESSITY FOR THEIR PROTECTION _Problem.--Man's relations to forests._ _(a) What is the value of forests to man?_ _(b) What can man do to prevent forest destruction?_ LABORATORY SUGGESTIONS Demonstration of some uses of wood. Optional exercise on structure of wood. Method of cutting determined by examination. Home work on study of furniture trim, etc. Visit to Museum to study some economic uses of wood. Visit to Museum or field trip to learn some common trees. [Illustration: A forest in North Carolina. (U. S. G. S.)]