The Control of Root Initiation and Development in Detached Cotyledons of Sinapis alba L. and Raphanus sativus L.

The initiation and development of root primordia in detached cotyledons of Sinapis alba (white mustard) and Raphanus sativus (radish) are studied, together with the inhibitory effects of sucrose and mineral nutrients on these processes. Root primordium initiation on petioles of excised mustard cotyledons cultured in petridishes in water commenced after 3 days and was completed after 5 days in culture, by which time a number of the primordia had extended and emerged from the petiole. Both sucrose and mineral nutrient solution had an inhibitory effect which was most marked when the cotyledonswere cultured in the solution from the time of excision. The total number of primordia initiated, their rate of development, and the final total number of emerged roots were all reduced. The later the time of transfer from water either to sucrose or to nutrient, the less marked the inhibition. Indeed, nutrient solution enhanced root growth in mustard when cotyledons were transferred after 5 days in water when root emergence had just commenced. The effects of sucrose and nutrients in relation to application before and after initial meristem formation has taken place are discussed, together with the ways in which these two solutions may exert their effect on root initiation and development.