Note F — PART I. RESPONSE OF PLANT ORGANS.

With reference to the fall of Mimosa leaf Jost says: “When the pressure of the cell decreases we naturally assume this to be due to a decreasing osmotic pressure due to alterations in the permeability of the plasma, and an excretion of materials from the cell. It is a remarkable fact that plasmolytic research (Hilburg 1881) affords no evidence of any decrease in osmotic pressure. No complete insight into the mechanism of the stimulus movement in Mimosa has yet been obtained, although one thing is certain, that there is a decrease in the expansive power on the under side of the articulation.”—Jost, “Plant Physiology”—English Translation, p. 515. Clarendon Press (1907). Blackman and Paine think that the loss of turgor on excitation “is probably due to the disappearance or inactivation of a considerable portion of the osmotic substances of the cells.”—Annals of Botany, Vol. XXXII, No. CXXXV, Jan. 1918.