The Interaction of Factors in the Growth of Lemna IV. The Influence of Minute Quantities of Organic Matter upon Growth and Reproduction

Abstract

Colonies of a pure clone of Lemna were grown under constant conditions of light and temp., and in an inorganic medium of constant pH, to which an extract of horse dung had been added in proportions of 0.2-20 parts per million. From day to day the growth of the colonies was measured, as indicated by increase in number of fronds, area, dry wt., etc. Although the plants will live indefinitely in a purely inorganic medium, a concentration of 2 parts in 10 million of the organic extract will significantly affect the growth rate. The organic matter acts as a stimulant, and is of the nature of a catalyst. The ash of the extract seems powerless to stimulate growth. The organic extract causes an increase in the size of the cells, and in the number of chloroplasts per frond. Hence the photosynthetic efficiency is increased, and the whole colony grows at a greater rate.