Auxin, the plant growth-hormone

Abstract

I. This continuation of the review on auxin in volume 1 of this journal is necessarily incomplete, for more than 500 papers have appeared on the subject in the last ten years, and space does not permit a more extended treatment. Only a few trends in the field will be enumerated, and whenever a number of papers on the subject have appeared in close sequence, usually only one or a few of them are listed, the choice being more or less arbitrary; availability of them in America, and sometimes priority or completeness in their exposition, have been used as criteria for selection. More stress is laid in this supplement on the theoretically important points than on the practical ones, since another review in this journal by Zimmerman on growth hormones has been announced; Zimmerman is one of the chief exponents of less theoretical treatment of the plant hormone field (38). Detailed information can be found elsewhere (8, 9, 31, 49, 56, 74, 84, 89), and the same subdivision will be followed here as in the original review, although the emphasis on subjects has shifted very much. II. The Avena method is still the principal method of quantitative analysis of auxins. A modification of it (61), the deseeded Avena test, is more sensitive to low concentrations and has been accepted as the standard test in some laboratories. Other qualitative and semiquantitative tests have been described in great number. Only the "green tissue tests" (38) and the pea test (76, 80) need be mentioned. Also, new auxin units have been introduced, W.A.E. of Boysen Jensen (9) and T.D.C. of Avery et al. (2), but they have exactly the same disadvantage as the A.E. of Kogl. They all depend on the relative sensitivity of Avena coleoptiles to auxin, which sensitivity varies with time of day, season, locality and laboratory. The only more or less absolute unit, although not ideal, is van Overbeek's (53) indoleacetic acid equivalent. It gives the amount of indoleacetic acid inducing the same curvature in the Avena test as the tested sample. III. Chemical isolation and identification nf indlneaetic acirl 1 Supplement to article in The Botanical Review 1: 162-182. 1935. 487