DEVELOPMENT OF THE LAMINA IN XANTHIUM ITALICUM REPRESENTED BY THE PLASTOCHRON INDEX

Abstract

Maksymowych, Roman (Villanova U., Villanova, Pa.), and Ralph O. Erickson. Development of the lamina in Xanthium italicum represented by the plastochron index. Amer. Jour. Bot. 47(6):51–459. Illus. 1960.—Xanthium plants were grown vegetatively, and leaves, whose developmental age was specified by a previously described leaf plastochron index (L.P.I.), were measured and studied histologically. Leaf initiation occurs before L.P.I.–6.0. Initiation of the lamina occurs at about L.P.I. –4.8, when the primordium is about 0.22 mm. long. Mitotic divisions in the marginal and plate meristems continue until about L.P.I. 1.7, when the leaf is about 37 mm. long, a period of about 23 days. Between L.P.I. 1.0 and 3.0, approximately, there is a rapid 4‐fold increase in thickness of the lamina, with development of the characteristic palisade and spongy mesophyll tissues. Virtually no further increase in thickness occurs after L.P.I. 4.0, but the lamina continues to increase in length until about L.P.I. 6.0, when it has reached a mature length of about 180 mm. A statistical analysis has been made of planes of division in the marginal meristem, which in some respects fails to support published histogenetic schemes for this meristem.