Allan Witztum

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BACKGROUND AND AIMS Cables composed of long, non-lignified fibre cells enclosed in a cover of much shorter thin-walled, crystal-containing cells traverse the air chambers (lacunae) in leaves of the taller species of Typha. The non-lignified fibre cables are anchored in diaphragms composed of stellate cells of aerenchyma tissue that segment the long air(More)
Spiral grain in trees is formed during the process of cell division and maturation within the vascular cambium (sensu lato). Much effort in the past half century has been put into elucidating the mechanism(s) involved. The most accepted view is that the dominant factor involves the pseudotransverse cell divisions during anticlinal (multiplicative) division(More)
Thin vertical leaves often manifest twist. Perhaps the most prominent example of this is in Typha sp., but such twist is also apparent in Narcissus, Pancratium and many other genera. Such a blade is often referred to as a "spiral leaf". We will indicate the mechanical advantage afforded to the leaf by this arrangement, i.e. that it permits the leaf to(More)
Twisting is a prevalent feature of long, thin vertical leaves; it has been shown that this twist contributes to the mechanical integrity of the leaf. We address the question as to how this twist comes about, and posit that it is a reflection of twist at a lower structural (geometric) level. The stiffness required for maintaining verticality in leaves is due(More)
The “wool” of bolbos ho eriophoros described by Theophrastus in his Historia plantarum or Enquiry into plants is the primary xylem of the bulb scales of Scilla hyacinthoides (Liliaceae). When bulb scales are pulled apart transversely the gyres of the helical secondary wall deposited on the thin primary wall of the waterconducting elements are stretched and(More)
The leaves of Typha are noteworthy in terms of their mechanical properties. We determined the mechanical properties of the fiber cables within the leaf. We found that in vegetative plants, the lignified fiber cables isolated from the leaf sheath and nonlignified fiber cables isolated from the leaf blade of Typha angustifolia differ in their diameter,(More)
It has long been recognized that density is the dominant parameter in determining the shrinkage behavior of wood; denser wood generally shrinks more from the green to oven dry condition. There exists a more or less linear relationship: ~28 times the specific gravity gives the percentage volume shrinkage. There are of course not insignificant deviations, but(More)
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