The morphology and anatomy of holdfasts and branching radicles of Arceuthobium pusillum cultured in vitro
Seeds of the eastern dwarf mistletoe, Arceuthobium pusillum Peck, were cultured on White's medium supplemented with coconut milk, casein hydrolysate, and indoleacetic acid (IAA) or 2,4-dichlorophenoxyacetic acid (2,4-D). Large holdfasts were obtained with 2,4-D. At first, growth of these holdfasts arose from a centrally located meristem, but later from growth centers near the periphery of the holdfasts. Reticulate thickening of the cell walls was observed in the center area of the holdfasts. With IAA, flat structures with branches or papillae were obtained. If the seeds were cultured with 2,4-D for 3 months and then with IAA, a number of holdfasts formed branches. Centers of meristematic activity developed occasionally where radicles and branches were subjected to pressure.