Studies in the Regeneration of Horseradish

Abstract

Regeneration has been studied in fragments of various sizes, and complete plants, together with the effect of externally-applied β-indolylacetic acid (I.A.A.). The main conclusions are as follows: (1) In the intact plant regeneration is inhibited by the growing crown; in cuttings, I.A.A. will reduce the rate of primordium-formation, but cannot entirely suppress it. (2) The bud/root ratio among differentiated primordia is about 0·5–0·9 in long cuttings; it rises sharply in cuttings less than 2 cm. long, and falls in the presence of I.A.A. Most, though probably not all, of the observations concerning this ratio can be explained on a simple auxin-level hypothesis. (3) I.A.A., at an appropriate concentration, depresses the extension of buds and promotes that of roots. On each cutting, only one (proximal) bud will normally extend—but this form of dominance cannot be exactly simulated by I.A.A., and more than one hormone seems to be involved. The results are discussed from the point of view of hormone theories of regeneration, and it is concluded that direct measurements of internal auxin-content will be essential before the phenomena can be interpreted with consistency.