ABSTRACT
This chapter deals with the handedness events noticed in the vascular cambium of both softwoods and hardwoods under relation to the so-called spiral grains in the wood. The cambium shows right (Z) or left (S) spiral alignments, respectively, causing right- and left-handed spiral grains. The events of the vascular cambium that are responsible for this right- and left-handedness are the directions of intrusive growth of fusiform initials, directions of pseudotransverse divisions in fusiform initials, directions of rays spitting, and direction of ray union. The magnitudes of spiral angle vary between taxa and also within the taxa with aging. The factors suggested for controlling spiral grains in woods are discussed, but most of them, including genetic factors, are proved to be not vital. Whether to call the grains spiral or helical is also discussed, and it is concluded that helical is the most appropriate term and not spiral.
