| Abstract: | Paolillo , Dominick J., Jr ., and Ernest M. Gifford , Jr . (U. California, Davis.) Plastochronic changes and the concept of apical initials in Ephedra altissima. Amer. Jour. Bot. 48(1): 8–16. Illus. 1961.—The occurrence of distal mitoses and the differentiation of derivatives of the distal cells of the apex of E. altissima are correlated with stages of the plastochronic cycle. The relative rates of growth of elements within the various regions of the apex are characterized in terms of elongation gradients. The numbers of mitoses found in median sections of individual apices are recorded. It is concluded that the distal zone is the source of all other cells of the apex and should be regarded as a zone of initials. The concept of “méristème d'attente” and “anneau initial” is discussed in relation to the observations made on E. altissima. |
