THE hypocotyl of Cucurbita, and, I suppose, of every plant whose cotyledons expand and act as leaves, is negatively geotropic in its ultimate reaction. When the hypocotyl is in any other position than the vertical, the under half of it grows more rapidly than the upper. This is regarded as a response to the unusual disposition of the burden of the parts of the hypocotyl, as they rest upon one another; and the seat of perceptivity and response is more specifically located in the green cortex.' The purpose of the reaction is to get the cotyledons into the light, which, when the seed germinates in the ground, will be accomplished by pushing them upward. Now it is evident without argument that an excess of growth of the under half of the hypocotyl will place its upper end in a vertical position, so that its further growth will be upward only in case the basal end is fixed in its position and the naturally upper end is free-a condition which is fulfilled in nature by a considerable growth of the root before the elongation of the shoot commences. Teleologically, perhaps phylogenetically, the geotropism of the shoot has been developed along lines of "lengthwise" propriety: i. e., in order to secure a particular linear arrangement of root, hypocotyl, cotyledon, etc. But in the individual plant today, according to Czapek's explanation (loc. cit.), which is the only rational one I am acquainted with, the response is to a disturbance of the normal "crosswise" arrangement, so that each growing part of the hypocotyl acts without reference to the parts more or less remote from the cotyledons. The question as to whether or not any trace of the development of geotropism remains in its manifestation in the present