The Nature of the Auxin in Tomato Stem Tips.

It is of considerable importance to know the chemical identity of the naturally occurring growth hormone or auxin. However, the natural auxin occurs in such small amounts in the plant that chemical isolation is difficult if not impossible. To overcome the difficulty of the low concentration plant materials have been sought which conitained an exceptionally high auxin concentration. As such, corn oil and malt (KdGL, ERXLEBEN and HAAGEN-SMIT, 6 and 7; HAAGEN-SMIT et al., 4) or immature corn kernels (AVERY, BERGER and SHALUCHA, 2, 3) have been chosen as materials for isolation. From the work of VAN OVERBEEK (15) it must be concluded, however, that the auxin in the kernels is not involved in growth of the mesocotyl and coleoptile. Whenever auxin has been extracted from growing organs the concentration was found to be very low (well below 0.1 mg./kg.). With such small concentrations and with limited amounts of tissue only indirect methods of identification of the auxin are possible. These indirect methods include: 1. Determination of the diffusion coefficient 2. Determination of alkali and acid sensitivity 3. Determination of light sensitivity. In the present investigation the diffusion coefficient of the auxin in the growing tip of tomato plants was determined, together with some additional evidence from acid and base sensitivity. Because it is not certain that the free or diffusible auxin is identical with the extractable auxin, the diffusion coefficient of both forms was determined. After auxin was diffused from tomato stem tips for 90 minutes, these tips were extracted for one hour with ether, and both auxin sources were investigated separately.