. Outlines of plant life : with special reference to form and function . Botany. 178 OUTLINES OF PLANT LIFE. Stimulated by the moisture, curve toward the damp sawdust. Upon entering it the stimulus ceases, and they start again to grow downward, being positively geotropic. Again the stimulus of the moist surface overcomes that of gravity, and they turn back to it, often threading themselves in and but of the wire gauze. Since only one-sided action of a stimulus J. Fig. T32.—Apparatus for demonstrating hydrotropism, a, a, a zinc dislc, witli hooks to which is attached a cylinder or trough of wir
. Outlines of plant life : with special reference to form and function . Botany. 178 OUTLINES OF PLANT LIFE. Stimulated by the moisture, curve toward the damp sawdust. Upon entering it the stimulus ceases, and they start again to grow downward, being positively geotropic. Again the stimulus of the moist surface overcomes that of gravity, and they turn back to it, often threading themselves in and but of the wire gauze. Since only one-sided action of a stimulus J. Fig. T32.—Apparatus for demonstrating hydrotropism, a, a, a zinc dislc, witli hooks to which is attached a cylinder or trough of wire netting filled with damp sawdust In this are planted peas, g^ whose roots, A,/, k, nt, first descend into the air but soon turn toward the damp sawdust again, w has threaded itself in and out of the netting.— After Sachs. determines direction of movement, if the air be saturated they continue to react to the stimulus of gravity alone. 251. (e) Movements due to contact.— Contact, either gentle or forcible, and friction act as stimuli to modify the growth of many plant parts. Only rarely is the main axis of a plant sensitive to mechanical stimuli, except, perhaps, to long continued contact (or pressure) in the case of some twining plants. But in many plants tendrils and leaf-stalks are irritable to contact, even to a degree far surpassing that of our nerves of touch. If the tip of a tendril (^225), while still capable of growth,. 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 Barnes, Charles Reid, 1858-1910. New York : Henry Holt and Company
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