Comparative Root Anatomy of Seminal and Nodal Root Axes of Summer Cereals with Special Reference to the Development of Hypodermis and Cortical Sclerenchyma

Abstract

Seminal and nodal root axes play an important role as conducting pathways for transporting substances into and out of roots. The anatomical feature of the tissue at the basal portion of these axes in nine species of cereals was examined with emphasis on the hypodermis and the cortical sclerenchyma. In the seminal root axes, none of the species examined developed cortical sclerenchyma except rice. In contrast, all the species developed the cortical sclerenchyma in the nodal root axes. This phenomenon was regarded as a type of heterorhizy. The hypodermis consisted of more regularly arranged cells in the nodal root axes than in seminal root axes in all the species. The marked wall thickening of the hypodermal cells in the nodal root axes was observed in Japanese barnyard millet, pearl millet and foxtail millet but not in the other species. Some specimens of Japanese barnyard millet showed wall thickening also in the epidermis. The number of cortical scleren-chymatous layers varied with the species. The cortical disintegration was observed in the nodal root axes of all the species. However, in the seminal root axes, among the species examined, only finger millet, pearl millet, and foxtail millet did not show cortical disintegration. In these three species, the tissues external to endodermis tended to be deformed and sloughed off in the seminal root axes. Finger millet developed a thickened-wall cortical layer encircling the endodermis.