Transport of Root-forming Hormone in Woody Cuttings.

It has been repeatedly observed since early times that if stems from some of our common woody plants are girdled, adventitious roots may be formed above the girdle. Although this regeneration phenomenon may result in part from an interruption of food transport, recent evidence indicates that the regeneration is controlled by hormones w^hich are transported in the phloem. The greater part of the experimental work on the nature and transport of these hormones in the plant has been done with Avena coleoptiles and pea (Pisum sativum) cuttings. WENT (12) demonstrated that a growth-promoting factor from Avena coleoptile tips will diffuse out of them into a layer of agar, and that decapitated coleoptiles will grow considerably faster if blocks of this agar are placed on the cut surfaces than if they are supplied with pure agar. The chemistry of this growth substance has been worked out especially by K6GL, HAAGEN SMIIT, AND ERXLEBEN (6, 7). Three different crystalline substances were isolated, which physiologically cannot be distinguished. They have been named auxin a (C18H,2O5) ; auxin b (C18H3004) ; and hetero-auxin (indole-3-acetic acid-C, HO LN).Later THIMANN (10, 11) found that synthetic hetero-auxin not onily promotes growth by cell elongation but also causes root formation on pea cuttings. COOPER (2) also has shown that hetero-auxin induces root formationi on lemon, fig, Acalypha, and Lantana stem cuttings, and ZIMIMERMAN and WILCOXON (17) have found that hetero-auxin causes local initiation of adventitious roots on stems and leaves of tomato and tobacco plants. Experimental work, especially by VAN DER WEY (15, 16), on the transport of auxin in Avena, has shown that auxin is transported basipitally only, and that it is intimately connected with life processes. To cover these facts WENT (13) proposed the theory that naturally occurring potential differences in coleoptiles and other organs (apical parts being negative to the basal parts) would produce an electrophoresis of the negatively charged ions of auxin toward the positive base. In addition, it was found by WENT (14) that the transport of substances causing root formation in Acalypha is rectilinear, rigorously polar, and independent of the transport of carbohydrates. In contrast to these results showing polar transport of hormones as a basis of the well-klnown morphological polarity in Avena, Acalypha, and other plants, HITCHCOCK and Zi3iMERMAN (5) observed no strictly polar movement of several synthetic com779