Farmers' Bulletins, Nos. 78, 86, 225, 344. U. S. Department of Agriculture.
Hodge, Nature Study and Life, Chaps. X, XX. 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. THE ORGANS OF NUTRITION IN PLANTS—THE SOIL AND ITS RELATION TO THE ROOTS
Problem.—What a plant takes from the soil and how it gets it.
(a) What determines the direction of growth of roots?
(b) How is the root built?
(c) How does a root absorb water?