Incense cedar leaves and acorn drawing9/13/2023 The functional relationship between differentiation and growth rate was most pronounced in the maturation of protoxylem elements, the development of Casparian strips in the endodermis, the development of suberin lamellae in the endodermis, and by the development of phi layers in the inner cortex. Although early differentiation of precursory phloem could be discerned almost as soon as early vacuolation of metaxylem, its recognition was more dependent upon subjective judgment. Graphs are presented to show the functional relationships between growth rate and the varying distances from the apical meristem at which the tissues of the root differentiate and mature. Roots whose apical cells retain their meristematic appearance are able to resume growth after a period of dormancy, whereas roots whose apical cells undergo vacuolation are likely to perish. During dormancy, the configuration of the initial region seems to indicate the existence of apical initial cells which coincide with a minimal constructional center, as determined by studies of cell lineage. With diminution in growth activity, the peak occurs closer to the quiescent center and the size of the meristem appears to diminish. During periods of maximum growth activity, the presence of a quiescent center is accentuated by a peak in number of divisions in adjacent tissues. Autoradiographs confirm the presence of a group of relatively inactive cells at the site of the apical initials. The anatomical features of active and dormant roots of incense-cedar seedlings are described and discussed in relation to various problems of differentiation and morphogenesis.
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