The apparatus described consists of 2 glass jars one resting on top of the other, with their contents in contact only through a capillary tube. The upper jar contains sand, the lower a nutrient soln. The nutrient soln. is made so acid (pH 2) by addition of conc. H2SO4 that undesired nodule bacteria cannot grow in it. The sand used in the upper vessel is mixed with dolomitic limestone, CaCO3, and superphosphate; the mixture is sufficiently alkaline to neutralize the nutrient soln. and to furnish conditions favorable for growth of plants. The sand can be planted with disinfected seeds or seedlings, and can be kept covered with a sterile dish during the early stages of growth; but all protection to avoid contamination may be withdrawn later, because no bacteria can reach the plants by way of the nutrient soln. no matter how often the latter needs to be renewed.