Aggregate rays in New Zealand Nothofagus blume (fagaceae) stem wood and their influence on vessel distribution

Abstract

Aggregate rays occur in the stem wood of Nothofagus solandri var. cliffortioides (Hook, f.) Poole (mountain beech), N. solandri var. solandri (Hook, f.) Oerst. (black beech), N. iruncata (Col.) Ckn. (hard beech), and N. fusca (Hook, f.) Oerst. (red beech), but not in N. menziesii (Hook, f.) Oerst. (silver beech). The composite structures visible in transversely sawn wood consist of groups of narrow xylem rays separated by fibres; vessels are frequently absent. The influence of aggregate rays on vessel distribution was studied using scanning electron microscopy and tested statistically. Indented growth ring boundaries are associated with the presence of aggregate rays. Aggregate rays occur in saplings. In larger trees aggregate rays taper out beyond 6 cm from the stem centre.