A technique is described whereby Lemna can be grown in continuously circulating culture solution under constant conditions of temp., light, and aeration. This technique can be employed for a study of the influence of such factors as temp., light, length of day, etc., upon growth, respiration, and assimilation. Methods are described for the analysis of the growth of Lemna into increase of area, dry wt. increase, and increase of C content. The errors involved in this analysis are considered and the results of certain tests illustrative of the technique are given.