Abstract
Discoloration was produced in the xylem of seedlings of white elm (Ulmus americana) by injection of ethanol and buffer solutions; this was similar to the discoloration produced in elms infected by Ceratocystis ulmi. Histological changes produced during infection were studied. The distribution of polyphenols in healthy and diseased elms was compared by histochemical tests; the strong reaction in cells that in later stages of infection showed browning is an indication that pathological discoloration is due to oxidized phenolic compounds. These may originate by synthesis or by degradation of existing substances. Their role in the disease development may be to interfere with the sap movement either by their action on living cells or by their participation in the occlusion of vessels, and they may act also as toxins.
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