Studies on the survival of dicotyledonous cormous weeds in ploughed fields.
The life history of Leontice leontopetalum was studied under field and controlled conditions in connection with its survival in ploughed fields. At germination the cotyledonary tube elongates rapidly downwards and this lowering of the seedling in the soil is of great importance for the survival of the plant. Emergence of the seedling above ground is very late so that the tip of the cotyledonary tube has already penetrated to a depth of 12-15 cm. After the seedling stage L. leontopetalum is incapable of changing its depth in the soil. From the second year on, the plants are static and no vegetative reproduction occurs. The corms do not produce contractile roots or any other means of depth adjustment and once they have been raised to the soil surface by modern methods of ploughing the population of L. leontopetalum decreases rapidly. Hence this weed which was once common in fields of south-western Israel is now found mainly on road verges and waste places. The behaviour of Bongardia chrysogonum and Astoma seselifolium, the two other dicotyledonous cormous weeds studied, was similar to that of L. leontopetalum. -M.Y.