. Plant life, considered with special references to form and function. Plant physiology. THE MOVEMENTS OF PLANTS. 20j of the wire gauze. Since only one-sided action of a stimulus determines direction of movement, if the air be saturated they continue to react to the stimulus of gravity alone. 293. (c) 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. Fig. 200.—Apparatus for demonstrating hydrotropism, a, a, a zinc d
. Plant life, considered with special references to form and function. Plant physiology. THE MOVEMENTS OF PLANTS. 20j of the wire gauze. Since only one-sided action of a stimulus determines direction of movement, if the air be saturated they continue to react to the stimulus of gravity alone. 293. (c) 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. Fig. 200.—Apparatus for demonstrating hydrotropism, a, a, a zinc disk, witli hooks to whicli is attached a cylinder or trough of wire netting filled wdth damp sawdust. In this are planted peas, ,i,^, whose roots, h, 7, k^ in. first descend into the air but soon turn toward the damp sawdust again. ;;/ has threaded itself in and out of the netting.— After Sachs. continued contact (or pressure) in the case of some twining plants. But in many plants lateral axes in the form of ten- drils (*|^ 115, 158) and leaf-stalks (*^ 157) are irritable to contact, even to a degree far surpassing that of our nerves of touch. If the tip of a tendril (^ 266), while still capable of growth, come in contact with a solid body, it will quickly become concave on the side touched, and thus will wrap about the object, if it be of suitable size. This curvature is due first to the shortening of the cells upon the concave side and later to unequal growth on opposite sides. Finally this effect. 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, H. Holt & company
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