On the inhibition of bud development and other functions of growth substance in vicia faba

Abstract It is well known that when the growing point of a young dicotyledonons plant is removed, the axillary buds lower down the stem grow out strongly, and eventually take the place of main stem. The presence of the terminal bud thus exercises an inhibiting action on the development of the lateral buds, causing them to remain dormant. To a smaller extent the leaves also inhibit the development of buds in their axils, as was shown by Dorsál (1909). The phenomenon has been studied by many workers, among others by Snow, who found (1929, a) that the rapidly growing young leaves in the terminal bud were the most active in inhibiting development of the axilllaries. It appears also, from our experiments, that the rapid growth of a lateral bud is accompanied by inhibition of the bud immediately below it, and a similar behaviour of opposite buds was observed by Dorsál (1926). In a brief preliminary communication (Thimann and Skoog, 1933) it was shown that the inhibiting action of the terminal bud can be imitated by applying the growth substance ("auxin" or "Wuchsstoff") to decapitated plants. These experiments, and others, will now be described more fully; further, the relation between the growth promoting action of growth substance and its effect on bud inhibition will be considered. The first evidence that the inhibition of lateral bud development might be caused by a special substance was brought forward by Snow (1929, b). The work to be described here proves that inhibition can be caused in this way, and shows that the inhibiting substance is almost certainly identical with the hgrowth substance. Literature on the growth substance need not be discussed here (see Nielsen, 1930; du Buy and Nuernbergk, 1932; Thimann and Bonner , 1933); it is only necessary to mention that the substance promotes growth by cell elongation and not by cell division. On this account it has been principally studied in the Avena coleoptile, in which it is produced in the tip and transported in a polar manner towards the base.