STUDIES ON THE GROWTH OF EXCISED ROOTS

Abstract

SummaryYeast extract was found to enhance the growth of the excised roots of a Czechoslovakian strain of groundsel. Effects of yeast extract were reproduced by a mixture of L(‐)‐tryptophane and DL‐methionine. β‐indolylacetic acid (IAA) had similar growth‐promoting effects to tryptophane.When roots were grown in medium containing either tryptophane or IAA for one passage and then subcultured into arginine medium they showed a marked stimulation of growth, particularly of their lateral roots. This growth stimulation, referred to as the ‘indirect’ effect of tryptophane and IAA, was greater than that observed when the roots were subculture into the same tryptophane or IAA medium for their second passage rather than into arginine medium.1‐naphthoxyacetic acid (1‐NOA) was not directly stimulatory in Passage 1 but caused an ‘indirect’ stimulation of growth in a subsequent passage in arginine medium. 2‐naphthoxyacetic acid (2‐NOA) caused a much greater ‘direct’ enhancement of growth in Passage 1 than tryptophane, methionine or IAA. This strong stimulation was also shown ‘indirectly’ after subculture of the roots into arginine medium.The hypothesis is advanced that the growth of excised roots from this strain of groundsel is limited by a suboptimal concentration of some natural auxin‐like substance.