VARIATIONS IN LEAF NUMBER IN HIPPURIS. A STUDY OF WHORLED PHYLLOTAXIS

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Abstract
The number of leaves per verticil in the material examined varied from 2 to 16. The variation in leaf number from verticil to verticil cannot be correlated to the splitting of primordia, junctional forces, binding whorls, acropetally developing forces from the stele, positions of leaf traces, nor to a constant angle between leaf insertions at every node. In tracing the development of leaves it is clear that nodes bearing leaves are produced in partially differentiated internodal tissue, as the apical thimble enlarges and grows. The leaves are not initiated at a constant distance from the tip and the larger the circumference of the leaf insertion disc, the larger is the number of leaves. The centers of the leaf primordia are circa 50 microns apart in each verticil. The initiation of leaves is traced in both aerial and aquatic apices using material from a single clone and also from a variety of sources. Aerial apices are usually smaller than aquatic ones and are of a different shape. However, the primordia are apparently the same until they are 50 microns long. Seven cells in the second layer divide periclinally to initiate each primordium. The study suggests that each of these groups of seven cells originates from anticlinal divisions of a single cell. The several cells separating the groups also originate from a single cell.

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