Experimental Morphology and Morphogenesis Then and Now: A Symposium in Memory of Elizabeth G. Cutter
Fisher, Jack , Blanco, Mario .
Tension wood fibers and variant secondary growth related to stem undulations in Bauhinia (Fabaceae) "monkey ladder" lianas.
The stems of many lianas (woody climbers) have unusual shapes and variant (also called anomalous) secondary growth. Possibly the most striking are some neotropical species of Bauhinia (Fabaceae; notably B. guianensis, B. glabra) known as “monkey ladder vines”. Their mature stems are often flattened and show extreme, regularly produced undulations. Each undulation encompasses the proximal and distal halves of two adjacent internodes, and the next undulation reverses the direction of curvature. We describe stem development in B. glabra and correlate the changes in stem shape with anatomy. Growing stems bear tendrils on short lateral branches and are initially straight with a uniform layer of inner secondary xylem (ISX) around a cruciform pith. ISX has narrow vessels and lignified fibers. Most stems become flattened and undulated with the first production of outer secondary xylem (OSX), which usually forms two lobes that are perpendicular to the two parastichies of the distichous phyllotaxy. OSX has wide vessels and only gelatinous fibers (G-fibers) with the structural appearance of tension wood fibers. Similar G-fibers are also present in the secondary phloem and also scattered within the cortical layer of sclereids. Measured transverse stem sections showed greater OSX and phloem on the concave sides, roughly correlated to the degree of undulation. Thus, the concave side of each undulation has a greater transverse area and quantity of G-fibers than the opposite convex side. Older stems that were not undulated had more lignified, symmetrical ISX and less lobed OSX than undulated stems. We conclude that uneven distribution of G-fibers (which produce tension) is involved in the progressive development of the undulations. Although young stems attach by lateral branch tendrils as they grow in length, older stems may maintain their position by using the undulations and the persistent bases of lateral branches (which are usually positioned just below the outer part of each undulation) as hooks.
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1 - University of British Columbia, Dept. of Botany, Vancouver, BC, Canada
2 - Universidad de Costa Rica, Escuela de Biología, San José, Costa Rica
monkey ladder vine.
Presentation Type: Symposium or Colloquium Presentation
Location: Delaware B/Hyatt
Date: Wednesday, July 11th, 2012
Time: 11:00 AM