Histological Responses of Vicia faba to Indoleacetic Acid

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Abstract
Plants of V. faba decapitated below the 5th node and treated with 1.5% indoleacetic acid in lanolin responded by the formation of small tumors. Every parenchymatous tissue becames active to some extent in the formation of the tumor. Epidermal and outer cortical cells enlarged radially; the inner cortical cells divided transversely, occasionally the outer cortical cells tangentially ; the cambium increased its activity and an interfascicular cambium was formed and became active as the early signs of response. Later parenchyma of the xylem, phloem, pericycle, pith, and rays became active to varying degrees. Pith cells gave rise to an internal callus, and in some cases a surface callus was formed by activity of cells in the vascular region and later of all parenchymatous regions. In later stages all the cells of the cortex became highly meristematic. Vascularization of derived tissues is extensive. The endo-dermal derivatives form a group of extravascular strands supplemented by an occasional strand formed in the peri-cycle or phloem. Small groups of wound tracheids are differentiated in the pith, pith callus, cortex, and surface callus when present. Root induction is uncommon but occasionally large, poorly organized masses of tissue are developed which are probably best interpreted as potential roots. Occasional polyploid nuclei are found in the large parenchymatous cells of the cortex and pith in both treated and control stems, although somewhat more numerously in the treated stems.