ACCUMULATION OF BORON BY RECIPROCALLY GRAFTED PLANTS

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Abstract
Plants show marked contrasts in the amount of B they accumulate. Some plant organs or parts accumulate much more B than others. Within parts there are likewise marked differences in B accumulation; the margins of lemon leaves may contain 30 times as high a cone, of B as the mid veins and petioles. It is believed that B is carried to the leaves by the transpiration stream as an inorganic radical and that much of it is there combined with organic compounds that are differentially mobile. The B cones, accumulating in the leaves of scions were directly influenced by the rootstock upon which they were grown. The B concs. in scion leaves were reduced if grafted to varieties normally accumulating lesser concentrations and increased when grafted to varieties normally accumulating higher concentrations. B cones, in the leaves of the scion tended to approach those normal to the rootstock variety. The comparisons were between reciprocally grafted sun-flower and Jerusalem artichoke and between lemon and Chinese box orange. Between the latter species the interchange of rootstock effected a 3-fold change in B concentration in the leaves. B absorption is not wholly contingent upon the rootstock employed. Eureka walnuts accumulated more B in their leaves than Payne walnuts when both were grafted on black walnut roots. Different citrus species accumulating comparable concentrations of boron in their leaves may show marked differences in the severity of injury. It is concluded that with other conditions equal the rate of B absorption is determined both (1) by the characteristics of the absorbing root cells and (2) by the nature of the B compounds in the plant and the equilibrium between mobile and non-mobile compounds.

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