The Vascular Pattern of Italian Ryegrass (Lolium multiflorum Lam.) 1. The Young Seedling and Its Variability

Abstract

The vascular system of the young Italian ryegrass seedling (Lolium multiflorwn Lam.) is very similar to that of oat (Avena) which has been described in the past. Early accounts however fail to record the distinctive separate course of the xylem and phloem constituents of the bundles at the coleoptilar node. The ascending mesocotylar trace is bicollateral. It continues up, in part, into the mid-vein of the first foliage leaf and arches over, joining the bases of the two coleoptilar traces, to become the collateral scutellar trace. Considerable variation exists from seedling to seedling in the details of the vascular pattern. This is coupled with additional variation in mesocotyl elongation, extent of the coleoptilar node, number and location of lateral root primordia and their maturation, rate of growth of coleoptile and first foliage leaves and the rate of vascular differentiation within them. Possible causes of this variability are discussed and it is noted that apparently identical plants, selected on a single morphological criterion such as degree of elongation of the coleoptile, may be expected to differ markedly in other morphological and anatomical aspects, influencing their performance in physiological experimentation.