COPPER AS AN ESSENTIAL FOR PLANT GROWTH

Abstract

The stimulating effect of copper on plant growth was noted early in the use of copper salts as fungicides. A few years ago FELIX (3) obtained improvement in the growth of certain plants on several peat soils by the application of copper sulphate, both to the soil and in solution to the leaves. ALLISON, BRYAN, and HUNTER (1) were able, by the use of copper sulphate, to produce crops on certain otherwise unproductive peats of the Florida Everglades. Other treatments, notably caustic lime, manganese sulphate, and manure also gave improvement, but were not so beneficial as copper sulphate. BRYAN (2) also obtained greening in chlorotic leaves of plants grown in this soil by treating them with solutions of copper sulphate or manganese sulphate. These investigations do not furnish final proof, how-ever, that copper is essential to plant growth. The work reported in this paper provides additional evidence on this point. Sunflowers, tomatoes, and flax were used in these investigations. One-liter pyrex beakers with paraffine-coated, plaster of Paris covers were used as containers for the solutions in which the plants were grown. All water used in making up the nutrient solutions was redistilled from pyrex. In the first experiment with sunflowers the salts used had been repurified for an earlier study (5) on the effects of the absence of boron on plant growth. These salts had been recrystallized from water from a copper still; this still had the usual block tin condenser. In later experiments the water used for the purification of the salts was redistilled from pyrex. The methods used for the repurification of the salts2 are described in a previous paper and will not be reiterated here.