Histological Changes in Bindweed and Sow Thistle Following Applications of 2,4-Dichlorophenoxyacetic Acid in Herbicidal Concentrations

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Abstract
Bindweed and sow thistle were treated with aqueous sprays of 2,4-dichlorophenoxyacetic acid at 1000 ppm. in 0.5% Carbowax 1500, applied during midsummer while the plants were growing vigorously. The responses of the plants were studied and the tissues examined to correlate histological changes with the death of the plants. In bindweed, pollen grains were plasmolyzed and disorganized, flowers were arrested in development, chlorophyll formation was checked, and cell division was activated in the large vascular bundles of the leaves. The majority of the cells in the leaves were plasmolyzed. Cell division was greatly increased in all cambial zones and phloem regions of the stem and rhizome of bindweed. Enlargement and rupture of cortical cells of the rhizome were conspicuous features. The root of bindweed responded more slowly to treatment than did other parts of the plant, so that changes which had occurred 7 days after treatment were of less intensity than in the rhizome but similar in nature. Starch disappeared from almost all parts of the flower of bindweed, but very little hydrolysis of starch occurred in the chloroplasts of the leaves. Disappearance of starch from the endodermis of the stem and the inner cortex of the rhizome and root were correlated with active cell division in the phloem region of those portions of the plant. In the rhizome of sow thistle, cells of the cortex were greatly enlarged and frequently torn. The periderm was ruptured, and dis-organized large-scale cell division occurred in the cambial zone and phloem regions. Starch hydrolysis was inhibited in vitro by the action of the acid.