1. Among Ranunculaceous and allied plants, medullary bundles are found in the aerial stem of following species or genera: Thalictrum spp, Delphinium spp, Anemone japonica, A. vitifolia, A. rivularis, Ranunculus chinensis, Cimicifug a, Aftemonopsis, Glaucidium, Hydrastis, Pbdophyllum, DiPhylleia.<BR>2. The medullary bundles may be divided into five types in respects of their course and origin (text-figs. A-E in p.xxx).<BR>Type I.(Fig. A) Large leaf trace strands become medullary immediately at a node, and descending downwards through the pith migrate gradually to the periphery. Trace strands from the perianth do not enter into the pith:-Delphinium spp., Thalietrum spp., Ranunculus chinensis, Cimicifuga foetida, Anemonopsis.<BR>Type II.(Fig. B) The same to type I, but trace strands from the perianth enter into the pith. These strands migrate outwards in the lower internode:-Anemone japonica, A.vitifolia, Glaucidium.<BR>Type III.(Fig. C) Leaf trace strands descend throughout the first internode, in the ordinary circle of the bundles and then enter into the pith in the second internode:-Hydrastis.<BR>Type IV.(Fig. D) Trace strands from the perianth occupy the central part of the pith throughout the stem:-Podophyllum, peltatum, Diphylleia Grayi.<BR>Type V.(Fig. E) Leaf trace strands are in periphery, the cauline bundles and the bundles from lateral shoots are in rather medullary part of the stem, being dominant in size:-Cimicifuga japonica.<BR>3. The differences of these types may or may not show the systematic affinities.<BR>4. The amplification of the leaf trace makes the medullary bundles indicated by the types I to IV differentiate, while the reduction causes the type V to appear. The type I derived probably from the ordinary dicotyledonous type, represents the most primary type, from which the type II may be derived. Types III and IV seem to be developed through the type II in two different directions, former probably in reducing in the direction of the type I.(Botanical Institute, Koishikawa, Tokyo)