Nutrition and the quiescent centre of root meristems.

Root apices were fed with tritiated thymidine from the endosperm and from labelled root caps placed on decapped roots. Supply from both sources reaches the meristem, but is attenuated by the demand of the dividing cells. The thymidine reaches the far sides of the quiescent centre from both directions. Starvation is thus unlikely to be the reason for the existence of the quiescent centre although cessation of mitosis in the normally meristematic regions may stimulate the quiescent centre by releasing nutrients.