1. On the occurrence of gelatinous fibres, with special reference to root wood. 2. Histological studies in the secondary xylem of species of Ephedra

Abstract

The occurence of reaction wood in numerous trees, small shrubs and herbs is described both in stems and roots, and the possible relation between gelatinous fibres and tension wood considered. In the roots of a number of dicotyledonous plants, gelatinous fibres were found to be abundant and more or less regularly distributed irrespective of the orientation of the organ with respect to gravity. It is suggested that gelatinous fibres, irrespective of their position in a stem or root and tension wood fibres are the cytological expression of the same phenomenon and should be considered as one type of fibre. The formation of tension wood bears less relation to the position of the ontogenetic centre of stems and roots than is generally thought. There was evidence that in horizontal branches, the distribution of tension wood fibres within a ring is more common in the early wood on the upper side and in the late wood on the lower side, but this is not invariable.The occurrence of gelatinous axial parenchyma in branch and root wood of robinia is recorded for the first time. Compression wood was not found in horizontally lying roots of a few gymnosperms examined.