ADVENTIVE EMBRYONY IN TISSUE CULTURES OF THE WILD CARROT,DAUCUS CAROTA

Cultures of callus tissue derived from roots, petioles, or umbellet peduncles of the wild carrot have been observed to form large numbers of adventive embryos which closely resemble ovular embryos of the same species. In the presence of cocoanut milk, which is not otherwise required in the nutrient medium, these embryos germinate and produce plants which may be normal in all respects. The sequence of forms in embryogenesis has been traced back to embryos of fewer than 10 cells, and the pattern of development has been found in many cases to correspond closely to that of ovular embryos, especially with respect to the early filamentous stages. The accumulation of granular starch in both the parenchymatous cells of the callus and in the embryos at certain stages of their development is a marked characteristic of differentiating callus. Investigation of the nutrient requirements of the callus tissue undergoing differentiation of embryos reveals that a wide latitude is possible in the composition of the basal medium, consisting of mineral salts, vitamins, and sucrose. Embryos form readily in tissue which has been extensively subcultured on a simple defined medium which consists of the basal medium plus adenine and 2,4-D. Tissues cultured on cocoanut milk and 2,4-D, or kinetin and 2,4-D, are more heterogeneous in composition and may contain, in addition to embryos, idioblastic tracheids, anthocyanin-pigmented cells, and complex vascularized nodules. Chemical control of alternative morphogenetic pathways, and of embryogenesis itself, is partially demonstrable.