Leaf Growth Hormones. I. A Bio-Assay and Source for Leaf Growth Factors

Abstract

1. The preliminary experiments in the formulation of a bio-assay for leaf growth factors and in the finding of a crude source of these factors are described. 2. A quantitative bio-assay for hormones controlling the growth of leaves is described. The general type of leaves and the method of using them are described, together with suitable methods for measuring the increased growth of isolated leaf sections. 3. The sources of these growth factors may be classified in two general types, seed diffusates and leaf extracts. Yeast extract was also found to be a good source of these factors. 4. The basic medium of the leaf test is described as a 1 per cent sucrose solution. This is used in order that the growth rate of the leaves may not be limited by sugar. Units and standards in the leaf test are described. A solution of "standard activity" is defined as well as a "leaf unit," 5. The general nature of the growth response to pea diffusate is discussed. In both Raphanus and Nicotiana there is an increase in area of the sections grown in pea diffusate, and an increase in thickness. Cell enlargement also appears to be greater, with a separation of the spongy parenchyma and formation of more intercellular air spaces.