Mechanisms of root penetration of seeds germinating on the soil surface

Methods used by seedlings to affix themselves to soil and to produce sufficient force to counterbalance the penetrating radicle, were studied. Seeds of five taxa-macaroni wheat, cucumber, lentil, bitter vetch and the sorghum hybrid Vidan-were sown on the surface of sand and sandy loam. Roots of lentil and bitter vetch did not affix themselves and penetrate into the soil. In lentil, putting weights on the seeds or transferring germinating seedlings to rims of holes, enabled subsequent root penetration. Roots of Vidan grew horizontally a few cm on the soil, and mostly in sandy loam anchoring by root hairs occurred, followed by a downturning of the root tip and penetration. A small viscous drop on the tips of Vidan root hairs apparently aids adherence to soil particles. In cucumber, the root hairs anchored first, followed by the thin lateral roots, and finally penetration of the main root occurred. In wheat, the three seminal roots supported each other during superficial penetration of their root tips and this enabled the root hairs to anchor, providing support for the further penetration of the roots in the soil.