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Two year old shoots of Salix fragilis L. were treated with morphactin and Ethrel to observe the influence of these compounds on xylem differentiation. Three treatments were used: I) morphactin IT 3456 was applied on 23 May 1976; 2) Ethrel on 23 May 1976; and 3) Ethrel on 20 June 1976. Each compound was applied in a lanolin paste as a ring around the shoot. The samples were collected at the end of the growjng season. Each treatment caused a pronounced swelling around the place of treatment. Both wood and bark were markedly influenced by the treatments. Anatomical analyses of xylem revealed: 1) a disorientation of cell types in all samples, 2) the formation of tyloses in all samples (with nucleated bud-type in the latter Ethrel treatment), 3) a general lack of vessels in the morphactin treatment, 4) the occurrence of crystals in longitudinal elements and highly lignified fibres immediately following both Ethrel treatments, and 5) the occurrence of areas of low birefringence immediately following the latter Ethrel treatment. These observations indicate the influence that these treatments have on xylem differentiation, primarily through an interference with endogenous hormones.

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The effect of morphactin IT 3456 on wood differentiation in <em>Carptinus betulus</em> and <em>Syringa vulgaris</em> was studied. In both species morphactin strongly stimulated production of wood but xylary differentiation was abnormal. Cellular differentiation was altered in that vessels were considerably smaller on transverse section and shorter than normal. Fibers and tracheids were also much ,shorter. It appeared that all cell types were disorientated from their longitudinal axis. It is probable that the effect of morphactin is caused by an inhibition of basipetal auxin transport and by the disturbance of general cell polarity during cambial divisions.