. A laboratory course in plant physiology. Plant physiology; Plant ecology. IRRITABLE RESPONSE 237 (c) Hydrotropism. The tendency of roots to seek wet places is a familiar phe- nomenon of the gardens and a manifestation of hydrotropism. For its study we ask first: What are the facts in a typical case 0} the turning 0} roots towards moisture? This may be tested by so arranging roots growing geotropically downward that they will be deflected, if sensitive, by a moist surface near them. _ Experiment. Select two flower-pots of 5-inch or 6-inch size; stopper both ends (Fig. 68), and by
. A laboratory course in plant physiology. Plant physiology; Plant ecology. IRRITABLE RESPONSE 237 (c) Hydrotropism. The tendency of roots to seek wet places is a familiar phe- nomenon of the gardens and a manifestation of hydrotropism. For its study we ask first: What are the facts in a typical case 0} the turning 0} roots towards moisture? This may be tested by so arranging roots growing geotropically downward that they will be deflected, if sensitive, by a moist surface near them. _ Experiment. Select two flower-pots of 5-inch or 6-inch size; stopper both ends (Fig. 68), and by aid of a round file. Arrangement for the study of hydrotropism; On the right is a cross-section of the flower-pot about its middle, saturated sphagnum instead of with water. It may be filled with worked in a carpenter's brace, bore a small hole near the upper mar- gin; tie lengthwise around, as in the figure, a double strip of cheese- cloth, between which and the pot place a number of soaked seeds- fill the pots with water (or pack them with very wet sphagnum) and suspend them in bell jars, one of which is to be kept with saturated atmosphere, while the other is to be given moderate humidity. Com- pare the positions of the roots in the two, and note approximately the critical angle at which the roots leave the moist surface. Other Methods. The arrangement described above serves admirably for this purpose, and permits very effective demonstration, all the better for the great contrast in color between roots and pot. It has the great advan-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Ganong, William Francis, 1864-1941. New York, H. Holt and Co.
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