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The use of 2,4-dichlorophenoxyacetic acid (2,4-D) as a selective herbicide has become quite extensive. In general, dicotyledonous plants are more sensitive to 2,4-D treatment than are most plants of the monocotyledonous types (7), although very little is known regarding the factors responsible for the difference in sensitivity. Recently, by using an isotopically labeled herbicide, Wood et al. (10) found that bean plants absorbed and translocated 2-iodo13"-3-nitrobenzoic acid (INBA) more readily than barley plants. Later, Mitchell et al. (8) extended their work to oat and corn plants. They suggested that the growth-inhibiting effect of INBA in the bean plant and its failure to produce significant inhibition in barley, oat and corn plants might be due to the differences in the manner in which INBA reacts with the plant constituents in each case.Gallup and Gustafson (3) using 2,4-dichloro-5-iodo'3l-phenoxyacetic acid were also able to demonstrate that the absorption of this growth regulator by the monocotyledonous plants is slower than by the dicotyledonous ones. The translocation to the apical portion of the plant is very rapid in broadleaved plants, but much less rapid in the grasses.Holley, Boyle and Hand (4) using carboxyl-C14-labeled 2,4-D demonstrated the presence of free 2,4-D in bean plant homogenate. Later Holley (5) using the same labeled preparation was able to show the presence of an ether-insoluble, water-soluble compound. Weintraub et al. (9), by using either carboxyl-or methylene-Cl4-labeled 2,4-D, demonstrated that the C14 from the applied 2,4-D in bean plants is incorporated into other substances within a few days. The radioactive carbon becomes distributed among a variety of plant constituents, including acids, sugar, dextrins, starch, pectin, protein and cell wall substances.In a publication from this laboratory (2) it was found that with bean plants the radioactive 2,4-D was readily absorbed and the radioactivity was found in various parts of the bean plant. In a continuation of this study (6) hours. An aliquot of each ground sample was analyzed for C14 by the usual wet combustion procedure.

PLANT PHYSIOLOGY rows of orchards than within the orchards, and the formation of precipitates of only slightly soluble salts on the surfaces of leaves in exposed positions. In the present studies this precipitation occurred on the leaves of the oranges sprayed for 1 second every 30 seconds, but there was none on the leaves under continuous irrigation. Continuous sprinkling is known to be practiced without injury in situations where the same water supply intermittently applied causes severe injury. SUMMARY Lemon and orange leaves accumulated more sodium and chloride when irrigated with sprinklers of the intermittent type during the day than they did when similarly irrigated during the night. They accumulated more when intermittently sprinkled than when continuously sprinkled. Intermittent sprinkling permitted evaporation and concentration of the salts in the water films left on the leaves. In advance of the measurements it was thought that little accumulation could be expected from the concentrations of salts in the initial irrigation water, and this proved to be the case.Comparisons were made of absorption by orange seedlings and by rooted lemon cuttings when the plants were inverted and the tops immersed for overnight periods in aerated single-salt solutions. Foliar absorptions by this procedure supported the earlier results and gave a constancy of cation accumulation except when there were heavy accumulations of chloride in association with particular cations.

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