STRUCTURE AND ONTOGENY OF LATICIFERS IN CICHORIUM INTYBUS (COMPOSITAE)

The branched anastomosed laticifer system in the primary body of Cichorium intybus L. originates in embryos from files of laticiferous members at the boundary between phloic procambium and ground meristem. Upon seed germination, laticiferous members develop perforations in the end walls which become entirely resorbed. Perforations also develop in the longitudinal walls of contiguous laticiferous members and from lateral connections between developing laticifer branches. Additional laticiferous members originate as procambium differentiation proceeds, and their differentiation follows a continuous acropetal sequence in leaf primordia of the plumule. In roots, laticifers closely associated with sieve tubes in the secondary phloem originate from derivatives of fusiform initials in the vascular cambium. These laticifers develop wall perforations and in a mature condition resemble laticifers in the primary body. As the girth of the root increases, laticifers toward the periphery, unlike associated sieve tubes, resist crushing and obliteration. Laticifers vary in width from about 4 to 22 μm; the widest ones occur in involucral bracts and the narrowest ones in florets. There was no evidence that intrusive growth occurs during development of the laticifer system, although such growth may occur during development of occasional branches which extend through ground tissue independent of phloem and terminate in contact with the epidermis. Presence of amorphous callose deposits is related to aging of laticifers and mechanical injury.