Ontogeny of the vascular bundle inZea Mays

does not appear. First page follows. Continuing the studies on the anatomy of crop plants, with special emphasis on vascular differentiation (Esau, 1936a, 1938, 1940, 1941),3 the writer has selected Zea Mays L. as a representative of the monocotyledons. Though the vascular system of this plant has often been studied (Strasburger, 1891, p. 329-63); (Hayward, 1938, chapter 5); (Sharman, 1942), the ontogeny of the vascular strand merits further detailed investigation in view of the many unsolved problems of vascular differentiation in the monocotyledons. (See review by Esau, 1943). The present paper concerns, first, the developmental relation between the vascular tissues and the bundle sheath—a structure characteristic of the vascular bundles in the Gramineae. Second, it attempts to elucidate the nature of the meristem producing the vascular bundles. Literature gives conflicting answers to the question whether this meristem—some or all of it—should be interpreted as procambium or cambium. (See review by Esau, 1943). The vigorous vegetative side shoots used as material for slides were obtained from the plants of the Golden Cross Bantam variety, growing in an open field. In preparing the permanent slides a common paraffin method (Esau, 1941) was followed. Free-hand sections were employed for examining the gross structural features. The Morphology of the Vascular Bundle For clarity the structure of the vascular system and of the mature vascular bundle will be considered before the ontogenetic details. Since the recent works on this subject (Hayward, 1938; Sharman, 1942) have not cited Strasburger’s (1891, p. 329-63) thorough treatment of the morphology of the vascular tissues in Zea Mays, his description is here reviewed in the light of the present observations and the findings of other investigators. The Vascular System.—In common with the other monocotyledons, Zea has numerous “parallel” vascular bundles in the leaf blade and the leaf sheath. (Since the bundles converge and fuse at the tip of the leaf, they are not truly parallel.) Large bundles alternate with small.