The Seedling Anatomy of Ipomoea batatas

Abstract

The primary root is tetrarch, and in the growing point 3 histogens may be observed. The plerome and periblem give rise to stele and cortex respectively, while the calyptrogen produces the root cap and by a final periclinal division forms the epidermis. In the development of the root, primary phloem is first differentiated and the enlargement of a single row of cells produces 4 primary latex vessels. Differentiation of lateral roots occurs early in ontogeny before the complete maturation of the protoxylem elements. In transition the primary xylem strands in the cotyledonary plane constitute the xylem of the midvein of the cotyledonary trace; while the intercotyledonary strands, by separation, form the xylem of the lateral bundles of the cotyledonary trace. The internal phloem arises later in ontogeny than the external and is not regularly connected with the external phloem by anastomoses. Some interconnection between the outer and inner phloem was observed in the petiolar region of the cotyledons. Infrequent cross connection of inner and outer phloem by differentiation of the intervening fundamental parenchyma cells was observed in the hypocotyl.