Occurrence of Reaction xylem in the peduncle of Couroupita Guianensis and Kigelia Pinnata

Abstract

The anatomy of the secondary xylem and distribution pattern of gelatinous fibres (G-fibres) have been studied in the developing and heavy fruit bearing mature peduncles of Kigelia pinnata and Couroupita guianensis. The peduncle in both the plants developed reaction xylem as a result of growth stresses caused by development of large fruits. In Couroupita peduncles which are originally horizontal, G-fibre distribution was unilateral and similar to that of typical tension wood whereas the hanging Kigelia peduncles have uniformly distributed gelatinous fibres throughout the xylem. The tension xylem severity was higher in the basal region and decreased towards the terminal region of the current year’s peduncle but after fruit development a drastic increase in tension wood severity was observed in the terminal region. In the Kigelia peduncles, tension wood severity in terms of G-layer proportion to lignified wall was found to be less than in Couroupita. The abundance of vessels decreased with high frequency of gelatinous fibres in Couroupita. The peduncle of Kigelia is characterized by high vessel frequency, thin normal fibre walls, and thick outer walls with thin gelatinous layer in tension wood fibres. Dimensional variations were also noticed in the mechanical and conducting elements varying with tension wood severity.