When subterranean clover (Trifolium subterraneum L.) plants were grown for 3 weeks over distilled water, tryptophan could be detected in the root medium of both sterile cultures and those inoculated with Rhizobium trifolii 3 days earlier. Auxin could be detected only in the inoculated medium. The auxin had the chromatographic and growth properties of indole·3-acetic acid (IAA). Since nodule bacteria produce auxin only in the presence of tryptophan, which is a probable precursor of lAA, it is suggested that the tryptophan exuded by clover roots is converted to lAA by nodule bacteria. Auxin was still produced in the root medium when strains of Rhizobium which do not nodulate subterranean olover roots were used as inooulant, or when nitrate, which delays nodulation, was present in the medium.Tryptophan, at high conoentrations, delayed nodule initiation in lucerne (Medicago sativa L.) plants grown on a mineral salts agar, while a-naphthaleneacetic aoid, an auxin, also delayed initiation, and in addition decreased the total number of nodules formed and prevented many plants from forming nodules. An antiauxin, p-chlorophenoxyisobutyric acid, did not influence nodule initiation, but increased the rate of nodulation and the total number of nodules formed per plant. A root growth promotor, a.(I-naphthylmethylsulphide)-propionic acid did not influence nodule initiation or number. Kinetin inhibited root growth, prevented some plants from nodulating, and reduced the number of nodules formed. Gibberellic acid slightly delayed nodule initiation, but greatly reduced nodule number, while root weight and nodule volume per plant were unchanged. Coconut milk inhibited nodule initiation.A possible mechanism of root-hair infection and nodule inception is discussed.

Ab8tractThe effects of endogenous factors (plant age, section length, and section location) and environmental factors (temperature and mineral nutrition) upon organ regeneration on isolated root sections of Ohondrilla juncea L. were used to develop a standard assay system for the study of the chemical regulation of regeneration. Bud and root formation and its polarity in the presence of a variety of regulators alone and in combinations were observed quantitatively. Bud numbers were increased by auxin (low concentrations), cytokinin, and gibberellin treatments. High concentra· tions of auxin inhibited bud formation and this effect was reversed by antiauxin, cytokinin, or gibberellin. Adenine did not counteract auxin· induced bud inhibition but adenine and N·6·benzyladenine did counteract inhibition induced by the purine antagonist 2,6·diaminopurine. Numbers of regenerated roots were increased by auxin treatment and reduced by cytokinin and gibberellin treatment. On control and auxin· treated sections, bud formation was strongly polar and proximal and cytokinin and gibberellin treatments lessened the polarity. Growth retardants inhibited regeneration. Of a number of synthetic auxins tested, 2,4.dichlorophenoxy. acet.O.methylhydroxamic acid and 4·amino.3,5,6.trichloropicolinic acid were the most effective inhibitors of bud formation.Mechanisms for the regulation of regeneration are inferred from the results.

All the isomeric thionaphthencarboxylic acids, except thionaphthen-4carboxylic acid, have been synthesised. Most of these syntheses involve intermediate formation of bromothioindoxyls by ring closure from the appropriate orth-substituted (bromophenylthio) acetic acids. Ring closure was facilitated by the presence of a formyl group or its equivalent in the ortho-position to a carboxyl or cyano-group.

A biological assay for substances inducing cell division is described. Blocks of tobacco stem pith were cultured aseptically on 1 ml of basal medium containing mineral salts, sucrose, and vitamins. The addition of auxin to the basal medium caused cell enlargement, but the addition of kinetin alone produced no reaction. Auxin and kinetin together induced cell division, l'esulting in nests of cells readily distinguishable visually from the original cells. Callus produced in this way could be subcultured indefinitely on medium containing bot,h 3-indolylacet,ic acid (IAA) and kinetin.When tobacco pith was cultured on basal medium plus IA..<\.., cell division was induced by extracts of a number of plant mel'istematic tissues added as supplements. Auxin was necessary for the reaction. Active extracts were obtained from fruitlet t.issues of apple, quince, pear, and plum harvested at various times after pollination.Extracts of seeds, placenta, and carpel wall of tomato at various stages of development were assayed for ability to induce cell division. Such ability was detected in extracts of cambium from stems of P1''nUS rnrliatn, Eucalyptus regnmlloi, and Nicotiana, tabacum.The cell-division response of tobacco pith to apple·fruitlet extract was not enhanced by the addition of polyols or casein hydrolysate, alone or in mixtures, to the culture medium. The response to kinetin wa!'; not enhanced b~' the addit.ion of nrea or sorbitol alone or in combination!';.

The extraction and partial purification of kinins from Pyrus malu.s cv. Granny Smith fruitlets are described. Tracing progress by means of a biological assay based on cell-division induction in tobacco pith, the kinins, extracted from fruitlets with aqueous ethanol, were partially purified by the following steps: (i) a.dsorption on a cation-exchange resin and displacement with ammonium hydroxide, (ii) adsorption on carbon and elution with pyridine-ethanol-ammonium hydroxide, and (iii) passage through a polyamide resin. When chl'omatographed on paper, the kinin ·activity in. the purified extract was resolved into at least foUl' zones, each having independent activity. The kinin of the most active zone was purified 900-fold.