Growth of Seedlings in Light and in Darkness in Relation to Available Nitrogen and Carbon

Abstract

Eighteen kinds of seed, varying widely in composition of their food reserves, were grown in sand, in light and in darkness, with and without addition of nitrate solution to the cultures. Wheat, barley, oats, rye, rice, corn, peas, beans, cow peas, soy beans, sunflower, squash, melon, and tomato were included. The type of food reserves influenced the character of growth of the seedlings. Seed with a high N and low C content produced seedlings with large tops in proportion to roots; those with low N and high C content produced seedlings with relatively small tops and large roots. The addition of nitrates favored the growth of shoots more than of roots, and was more effective in light than in darkness. Light favored the growth of roots, presumably by maintaining a high carbohydrate supply in the seedlings. Seedlings from high-protein seeds benefited most from the light, and especially when nitrate was added. These responses agree with results obtained earlier from tomato cuttings of different composition. The tissues of seedlings with limited N supply rapidly differentiated and matured in the light. Light favored secondary thickening of cell walls in both stems and roots.