Anomalous Secondary Thickening in Phytolacca americana L. (Phytolaccaceae)
1979; Wiley; Volume: 66; Issue: 9 Linguagem: Inglês
10.2307/2442563
ISSN1537-2197
Autores Tópico(s)Plant Taxonomy and Phylogenetics
ResumoAmerican Journal of BotanyVolume 66, Issue 9 p. 997-1005 Article ANOMALOUS SECONDARY THICKENING IN PHYTOLACCA AMERICANA L. (PHYTOLACCACEAE) Jan E. Mikesell, Jan E. Mikesell Department of Biology, Gettysburg College, Gettysburg, Pennsylvania, 17325Search for more papers by this author Jan E. Mikesell, Jan E. Mikesell Department of Biology, Gettysburg College, Gettysburg, Pennsylvania, 17325Search for more papers by this author First published: 01 October 1979 https://doi.org/10.1002/j.1537-2197.1979.tb06314.xCitations: 11AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Abstract Differentiation of the primary thickening meristem (PTM) was investigated in seedlings and older plants of Phytolacca americana L. Initiation of the PTM occurs in pericycle or inner cortex at the hypocotyl-primary root junction of young plants. Differentiation of the PTM in stems occurs acropetally in a cylinder of randomly dividing cells termed the diffuse lateral meristem (DLM). The PTM produces secondary tissue to the inside (internal conjunctive tissue) and to the outside (external conjunctive tissue). Patches of xylem and phloem differentiate, opposite each other, in recently produced internal and external conjunctive tissue, respectively. The resulting strands (desmogen strands) of xylem and phloem are secondary in origin, and are peripheral to primary vascular tissues. Phloem of desmogen strands usually differentiates first. Xylem of desmogen strands is composed of both tracheids and vessel elements; the latter sometimes becoming occluded with tyloses and unidentified substances. As root and hypocotyl increase in diameter, cylinders of PTMs differentiate successively and centrifugally in external conjunctive tissue. Even though the first PTM differentiates in pericycle or inner cortex and later PTMs differentiate in external conjunctive tissue, all are referred to as PTMs because of their similar activity. Multiple rings of desmogen strands can be observed in transections of lateral roots, primary roots and hypocotyls. Throughout the length of the stem, only one ring of desmogen strands is present. Fewer rings of desmogen strands are present in the top of the hypocotyl and cotylendonary node, as compared to the subjacent hypocotyl, due to anastomoses of centrifugally differentiating desmogen strands. Citing Literature Volume66, Issue9October 1979Pages 997-1005 RelatedInformation
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