Woods with included phloem: Heimer Llodendron Brunonianum and Avicennia Resinifera

Abstract

Summary The principal differences between the cambium of Heimerliodendron and that of a normal dicotyledon are: (a) the differentiation of longitudinal strands of phloem within the zone of meristematic cells, and (b) the absence of a permanent initial layer. Evidence for these differences is derived from longitudinal radial and tangential sections. Secondary thickening in A vicennia is due to a succession of cambia, each of which functions in a normal manner, but for a limited time. The first of these supernumary cambia arises by divisions of the inner cells of the cortex, but subsequent cambia in Avicennia arise within derivatives of the preceding cambium. A comparison of the cambium in these two ,enera emphasises that the secondary thickening of Heimerliodendron is of a distinctive type.