Studies on Root System Formation in Leguminous Crop Plants : 4. Anatomical observation of vascular system and origination of roots in hypocotyl and main root

Abstract

1. Anatomical studies were carried out upon the vascular differentiation in hypocotyl and main root mainly from the view point of root origination in leguminous crops. Ten species of epigeous dicotyledons and four species of hypogeous ones were used as materials in this study. 2. The root xylem of all the species shows various types from diarch to hexarch (fig. 1). Above all, two kinds of tetrarch and pentarch were observed in Vicia faba L. (fig. 1-9, 10) and also tetrarch and hexarch in Phaseolus vulgaris L. (fig. 1-4, 5). The triarch crops were found in the hypogeous group (fig. 1-11, 12). 3. The raws of secondary root were observed in the same number of xylems inside around the main root because the root primordia were formed by division of pericyclic cells opposite to the protoxylem. 4. As to the differentiation of vascular bundle system, a moderate degree of difference existed between the epigeal type and hypogeal one. (1) In epigeous dicotyledons, transition of bundles occurred and completed at the lowest part of the hypocotyl where perfect collateral bundle was recognized. Vascular bundles of lupine, peanut and soybean were seen to branch in the hypocotyl and the number of bundles, therefore, increased gradually (fig. 3-1, 2, 3, ). (2) In hypogeous dicotyledons, the transition region is comparatively long and extends to the upper first internode or second internode and the arrangement of vascular bundle as in root was still found in the hypocotyl (fig. 5-1, 2, 3). 5. In case of collateral bundle the adventitious roots originated in the interfacicular parenchyma and in case of imperfect collateral bundle in the transition region, it originated from the parenchyma laid among the phloems.