Histological Studies on the Root of Melilotus alba

Abstract

1. The ontogeny of the primary root of Melilotus alba is of the fourth angiospermous type of Janczewski, in which there is a general meristem from which arises the cortex, stele, and central portion of the root cap. The meristem is extended laterally to form the outer parts of the root cap, and at higher levels a dermatogen. 2. Protophloem is the earliest stelar tissue differentiated. 3. Secondary roots arise by cell divisions in the pericycle opposite the protoxylem ridges. The endodermis forms a temporary root cap, which is ultimately crushed or digested, as are also cells of the cortex and epidermis of the primary root by the emerging root. The vascular system is developed in a manner similar to the primary root. 4. Lateral roots develop in the periderm and primary rays of old roots and of the hypocotyl. Cells of the periderm, by radial and tangential divisions, give rise to a temporary sheath over the young root, which is later ruptured. Subsequent development is similar to that of the secondary roots...