On unusual wood structures in Scrophulariaceae

The Scrophulariaceae, though chiefly a family of herbaceous plants, contain also a number of genera with trees ( Paulownia and Wightia) and genera with species of suffruticose and fruticose habit. My colleague Mr. A. M. Cleef, who is studying the vegetation of the high Andean parts of Colombia collected material of the small genus Aragoa, endemic in the paramos of the Colombian and Venezuelan Andes. Though this genus consists in the main of small broomlike shrubs, a new species, Aragoa perez-arbelaeziana Romero, discovered by him, is a small tree, of which the stem reaches a diameter of 8 cm. The wood of Aragoa of which the structure was so far unknown, proved to be noteworthy because of the complete absence of rays and parenchyma. There was no indication at all of growth rings, and the vessels can not be distinguished from the fibres as seen on a cross section, as both are of equal width. In longitudinal sections vessels become recognizable by their simple perforations, their spiral thickenings and the presence of a few simple pits; whereas the fibre tracheids lack the spiral thickenings, and possess numerous bordered pits on both the radial and tangential walls. The diameter of the vessels and fibres varies in the 5 species investigated by me between 16 and 24 μm; the length of the vessel members is on the average 260 (185-370) μm and that of the fibre tracheids 310 (220-450) μm. This unusual wood structure was found not only in the small stems with a diameter of 4-8 mm, but also in the stem of the only arboreous species.