Gelatinous fibers, which may have tensile properties, are uniquely extra-xylary and may be primary or secondary. Three types exist in both orthotropic and plagiotropic axes, two in the cortex and one in the secondary phloem. In all axes they occur circumferentially in the outer cortex and may be important in stiffening the internode because mechanical tissues are otherwise not well represented. Subsequently in leaning stems or displaced horizontal axes they can be produced eccentrically (on the upper side) from initials that undergo considerable extension by intrusive growth. In the absence of the gravimorphic stimulus these cells remain undifferentiated. Gelatinous fibers continue to differentiate from cambial derivatives in the secondary phloem, again with considerable intrusive growth. A fourth similar type of cell occurs in petioles, but these fibers are short and may not be involved in petiolar torsion. All these fibers have the same distinct cytological condition. Gelatinous fibers show the characteristic late development of the Sg layer, separated from the primary wall as in tension wood fibers. Laticifers, a unique feature for gymnosperms, differentiate very early and can be distinguished readily from fiber initials.

Key words: eccentric growth, Gnetum, reaction anatomy, tension fibers