A Concentration Gradient in Corn Stalks

In a recent paper, Evelyn I. Fernald 1 has shown that the osmotic concentration of the sap of different portions of stems is correlated with the tendency of buds to develop on those portions. She has found by freezing point measurements on the expressed sap that in actively growing stems of privet, chestnut, Pkiladelphus, and Bryophyllum there is a concentration gradient, the highest concentration being in the apical portions, the lowest in the basal portions. In connection with these findings of Fernald on dicotyledonous stems, some measurements of the specific gravity of juice expressed from successive internodes of the corn stalk may be of interest. The plants used in this study were all vigorous, 8 to 11 feet high, with large but immature ears. The juice from single internodes was expressed for the specific gravity measurements, except in the upper portions of the stalks where it was always necessary to take two or more adjacent internodes as one sample in order to obtain enough juice. Occasionally, also, the two basal internodes were expressed together, as indicated by brackets in the table. After removal of the tough cortex, the tissue was thoroughly crushed in a food chopper. The juice was squeezed from the. pulp by hand through a muslin cloth, and filtered until clear through a folded filter paper. Precautions against evaporation were observed throughout. The specific gravity of the juice was determined by means of a small pycnometer in the form of a glass capsule with capillary intake and outlet tubes. A second weighing of the pycnometer filled with juice refiltered through the same paper constituted a check on each measure-