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Application of indoleacetic acid (IAA) and other auxins causes cultured radish (Raphanus sativus L. 'Scarlet Globe') seedling root segments to produce an increased frequency (FR, no. cm ') of lateral roots (LR); in the absence of auxin, segments spontaneously form about 6 LR cm-'. A dose-response study has revealed that the increase in FR follows a biphasic Michaelis-Menten relationship with the medium concentration of the undissociated form of IAA ([IAAH] MATERIALS AND METHODSRadish (Raphanus sativus L. 'Scarlet Globe') seeds were germinated in the dark at 24°C. After 3 d, root segments were excised between 0.5 and 3 cm behind the tip. Four segments were inoculated into 25 ml of medium contained in 125 ml Erlenmeyer flasks. Three or more replicate flasks were used for each treatment. The culture medium consisted of MurashigeSkoog salts (14), 88 mm sucrose, and 10 mm Mes and/or 10 mM succinic acid. Mes was used to buffer pH in the range 5.5 to 6.5, while succinic acid was used for the range 4 to 5.5; both were added to the medium when the pH was varied across the two ranges. Autoclaving caused pHm to change by as much as 0.

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(8) with the zinc concentration reduced by a factor of 10, 3% w/v sucrose, 0.1 mg/l of NAA, 100 mg/I of myoinositol, 0.2 mg/l of glycine, 0.5 mg/l of nicotinamide, 0.5 mg/l of pyridoxine, 0.5 mg/l of thiamine, and 0.1 mg/l of p-aminobenzoic acid. Cultures were grown in 250-ml Erlenmeyer flasks with 50 ml of medium, or in 125-ml Erlenmeyer flasks with 20 ml, on a reciprocating shaker (108 strokes/min, stroke amplitude 2 cm) in dim (5 ft-c) light at 25 to 28 C. During the 3-week subculture period, branches formed on inoculated segments, and the branches extended 2 to 4 cm in length. These branches did not form secondary branches within the 3-week subculture period. Segments (1-cm long) cut from the branches in a 3-week-old culture were used as inocula, either for subculturing or, after rinsing with distilled water, in experiments. Three to five segments were used per flask.Assessment of Results. In most of the experiments reported here, the number of branches initiated in a given time interval was the response measured. Segments were generally harvested 1 Abbreviations: NAA: ca-naphthalene acetic acid; BA: benzyladenine.www.plantphysiol.org on May 11, 2018 -Published by Downloaded from

Variation in long‐continued cultures of Haplopappus gracilis and Daucus carota has been investigated. A strain of carrot tissue was isolated that grew with a compact habit, in contrast to the highly friable habit of the parent strain. Its dividing cells were arranged quite differently than in the parent strain. Earlier work had shown that Haplopappus cultures could be reversibly altered in their pigmentation and form, by changing the culture medium. This was confirmed, and it was further shown that pronounced changes in nitrogenous compounds also occurred in response to factors in the medium. However, strains of Haplopappus were isolated which differed persistently from the parent strain, even when they were maintained under the same conditions. The variant strains, grown in the same medium, showed differences in their content of nitrogenous compounds. Stock cultures also changed spontaneously with time with respect to their content of nitrogenous substances. Acriflavine, at low concentration, inhibited the growth and formation of colonics by cells plated on nutrient agar, but, by prolonged exposure to sublethal amounts of the drug, resistant strains were isolated. Certain of the spontaneous variant strains were found to differ from each other and from the parent strain in their chromosome complements in ways that are described and to which the observed changes in morphology and metabolism of the cultures may be attributed. The variations that may occur in the free cells in culture are contrasted with the greater uniformity of the cells as they exist in the plant body.