OBSERVATIONS ON SPIRAL GRAIN IN TIMBER

Abstract

OCCASIONALLY THE elongated elements of the wood in a tree lie rather uniformly at an angle to the long axis of the stem; this arrangement naturally affects the properties of the timber and is spoken of as spiral grain.2 For -some years observations have been made in these laboratories, as opportunity permitted, upon the grain in wood, and in particular study has been made (Misra, 1939) of spiral grain in softwoods (Conifers). The writer had gained the impression from these studies that a similar type of grain rarely occurred in hardwoods (Dicotyledons), though other types of grain seemed to have been incorrectly reported as spiral grain on several occasions. In 1942, however, the removal of iron railings in a street near the University of Leeds, England, drew attention to a trunk of elder (Sambucus nigra L.) that seemed to be a clear example of spiral grain. While this trunk was being intensively studied, other elder stems were found showing similar structure, and examples of spiral grain in other hardwood species were also found in and near Leeds. It transpires, however, that such spiral grain in hardwoods differs in fundamental points from the apparently similar phenomenon in softwoods, and a comparison of the two types of spiral grain is therefore attempted in the following pages. While it is naturally impossible to make broad generalizations from the comparatively few specimens studied here, certain tentative suggestions can be made as to the factors associated during growth with the ultimate production of spiral grain. It seems desirable to preface the present observations upon spiral grain in hardwoods, a subject that has so far received little attention, with a brief statement of the characteristics of spiral, or twisted, grain in softwoods. Examples of spiral grain in softwoods have frequently been recorded and studied, but the observations require re-examination after considering the apparently related phenomena in the hardwoods. SPIRAL GRAIN IN THE SOFTWOOD.-A very full account of this type of wood, as it occurs in the Indian chir pine (Pinus longifolia Roxburgh) is given by Champion (1925) and the literature prior to that date is fully cited. Our observations, in particular many made by Misra (1939), first in this country and then in India on the same species, support in the main the generalizations of Champion. We are in complete agreement that the wood of the