. Elementary botany. Botany. 9° PHYSIOLOGY. 209. Transmission of the stimulus.—The transmission of the stimulus in this mimosa from one part of the plant has been found to be along the cells of the bast. 210. Cause of the movement.—The movement is caused by a sudden loss of turgidity on the part of the cells in one portion of the pulvinus, as the cushion is called. In the case of the large pulvinus at the base of the petiole this loss of turgidity is in the cells of the lower surface. There is a sudden change in the condition of the protoplasm of the cells here so that they lose a large part o
. Elementary botany. Botany. 9° PHYSIOLOGY. 209. Transmission of the stimulus.—The transmission of the stimulus in this mimosa from one part of the plant has been found to be along the cells of the bast. 210. Cause of the movement.—The movement is caused by a sudden loss of turgidity on the part of the cells in one portion of the pulvinus, as the cushion is called. In the case of the large pulvinus at the base of the petiole this loss of turgidity is in the cells of the lower surface. There is a sudden change in the condition of the protoplasm of the cells here so that they lose a large part of their water. This can be seen if with a sharp knife we cut off the petiole just above the pulvinus before move- ment takes place. A drop of liquid exudes from the cells of the lower side. 211. Paraheliotropism of the leaves of the sensitive plant.—If the mimosa plant is placed in very intense light the leaflets will turn their edges toward the incidence of the rays of light. This is also true of other plants in intense light, and isparaheliotropism. Transpiration is thus lessened, and chlorophyll is protected from too intense light. We thus see that variations in the intensity of light have an important influence in modifying movements. Variations in temperature also exert a considerable influence, rapid elevation of temperature causing certain flowers to open, and falling temperature causing them to close. 212. Sensitiveness of insec- tivorous plants. — The Venus fly-trap(Dionaea muscipula)and the sundew (drosera) are in- teresting examples of sensitive plants, since the leaves close in response to the stimulus from Fig Leaf of Venus tlv trap (Dionaea musci- puia). showing winged fietiolc and loomed obes. Fig. 84. 1 eaf of Drosera ro- tundifolia, some of the glandular hairs Folding inward as a result ol a stimulus. 213. Hydrotropism. — Roots are sensitive to mois- ture. They will turn toward moisture. 'This is of the greatest importance for the well-bein
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