RELATION BETWEEN ROOT RESPIRATION AND ABSORPTION

Abstract

Various theories have been developed to explain the nature of the absorption of water by roots, embodying what may be called imbibitional, osmotic, and passive forces (Miller 9). Imbibitional forces have been emphasized and shown to be of great importance by Shull (15) and others. Although Kunkel (7) assumed only imbibitional forces to be effective, more recent investigators agree that osmotic forces must also play an important part. But even these forces fail to explain satisfactorily the transference of water across the endodermis into the vascular cylinder. The nature of the Casparian strip seems to indicate that the transfer of water across this region is under the control of the living cells (Priestley 12, 13, 14). Also the effect of changing environmental conditions led Blackman (1) to believe that vital relations of the cell, involving the transfer of energy, must be concerned in absorption. Such energy changes would of necessity be manifested at some time in the respiratory processes of the root. There is no direct evidence showing a correlation between the respirational and absorptive activity of the root except that of Newton (10, 11), who found that the evolution of carbon dioxide varied with transpiration and with the osmotic concentration of salt solution supplied in the field. The present study was made to determine more accurately the relation between these processes, using plants under strictly controlled conditions. In order to reduce individual variations as far as possible, seed from a pure strain of corn (Funk's hybrid no. 517, Yellow Dent) was used in all the experiments. The seeds were placed in water for 12 hours, treated with 4 per cent, formalin for 10 minutes, and washed with sterile water. For germination they were placed under sterile conditions in petri dishes containing filter paper moistened with a few cubic centimeters of culture solution. This treatment resulted in normal and vigorous germination. When the radicles had reached a length of 1-2 cm. the seeds were placed on perforated sheets of cork which were floated in large dishes of Knop's solution. The solution was replaced at intervals of three to five days and continuously aerated. The corn plants were kept in the laboratory at full daylight illumination and grown in the cultures one to two weeks unti] needed.