The wide use of the auxin, indoleacetic acid, in physiological and biochemical experiments has promoted interest in methods for its colorimetric estimation. MITCHELL and BRUNSTETTER (1) have proposed both the nitrite and the ferric chloride-sulphuric acid tests for the quantitative estimation of indoleacetic acid (IAA) in aqueous solutions, basing their suggested procedures upon a study of optimal reaction conditions for these two reagents. According to them, the nitrite method is sensitive to 10 ug. IAA/ml. and develops a red color that is stable after two hours. In several attempts to duplicate their nitrite method using solutions of IAA varying from 20 to 45 pg./ml., we could not obtain a stable red color with IAA at the two hours proposed, or at any other time. A faint pink develops almost immediately which rapidly fades to orange or yellow, depending on IAA concentrations, within j hour. If the concentration of nitrite is reduced, the red color becomes sufficiently persistent to be read. Indole likewise gives a strong, relatively stable, red color in this test (cf.

No abstract

No abstract

Abstract. The magnitude of acceleration required to induce growth responses in Avena seedlings grown in the absence of tropic response to earth gravity has been investigated. For this purpose, a clinostiat was developed that imposes accelerations from about 10-9 g to 3 g upon the seedling; simultaneously, it nullifies, or compensates for, response to the directional component of the gravitational-force vector by rotating the seedling on a horizontal axis. When accelerations less than 10-? g are applied in either the acropetal or the basipetal direction, the growth in length and weight of the various organs is not maferiallv different from that of compensated seedlings to whicih no longitudinal force is applied. At accelerations between 10-: and 10 2 g, differences in growth become highly significant. When the centrifugal forces are transverse to the seedling during compensation, the threshold acceleration range for 4eoperception, as manifest bv shoot reorientation, is again between 10-3 and 10-2 g.Geotropic reorientation of the root becomes apparent after exposures between 10-4 and 10-3 g.In the contained environment of a satellite or interplanetary vehiicle, the apparently unique enxlironmental faoto,r is that of prolonged weiightless-

No abstract