Primary xylem maturation in conifer [Pinus virginiana, Thuja orientalis, Cryptomeria japonica] seedlings

• Published in: Botanical gazette (Chicago, Ill.) Ill.), 1976-01, Vol.137 (2), p.165-178
• Main Authors: Tilton, B.R, Palser, B.F
• Format: Article
• Language: English
• Subjects: Conifers; Cotyledons; Cryptomeria japonica; Embryos; Epicotyls; Hypocotyls; Orientalism; Phloem; Pinus virginiana; Platycladus orientalis; Seedlings; Tracheids; Xylem
• ISSN: 0006-8071; 1940-1205
• DOI: 10.1086/336856

Characteristics of primary xylem of seedlings of Pinus virginiana Mill., Thuja orientalis L., and Cryptomeria japonica D. Don were observed, with particular regard to the patterns of xylem maturation. Observations of serial cross sections of seedlings stained with safranin and fast green were correlated with those of whole specimens cleared by successive treatment with NaOH, chloral hydrate, and lactic acid. Embryos of all three species lacked mature tracheary elements. In germinating seedlings the locus of the first mature tracheid was in the cotyledons or simultaneously in the cotyledons and at the cotyledonary node in P. virginiana, nearly simultaneously in the cotyledons and hypocotyl-radicle in T. orientalis, and in the radicle or simultaneously in the radicle and at the cotyledonary node in C. japonica. The pattern of maturation of epicotyl tracheids was similar in all three species. The first mature epicotyl elements were located in the axis just above the hypocotyl strands; the initial discontinuity was obliterated as elements matured acropetally toward the primary leaves and basipetally into the hypocotyl. In all three species, vascular transition occurred between root and cotyledons. The morphology of primary xylem elements was similar in all three species. The earliest mature elements of T. orientalis and P. virginiana had helical secondary wall thickenings with scattered bordered pits; in C. japonica they had helical thickenings only. Later in ontogeny there appeared tracheids with reticulate thickenings and bordered pits, and still later, with bordered pits only. Removal of all or part of the megagametophyte from around the embryo did not delay or alter the pattern of early xylem maturation in surviving T. orientalis seedlings.