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

The vascular system of the young Italian ryegrass seedling (Loliummultiflorwn Lam.) is very similar to that of oat (Avena) whichhas been described in the past. Early accounts however failto record the distinctive separate course of the xylem and phloemconstituents of the bundles at the coleoptilar node. The ascendingmesocotylar 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 thecollateral scutellar trace. Considerable variation exists from seedling to seedling in thedetails of the vascular pattern. This is coupled with additionalvariation in mesocotyl elongation, extent of the coleoptilarnode, number and location of lateral root primordia and theirmaturation, rate of growth of coleoptile and first foliage leavesand the rate of vascular differentiation within them. Possiblecauses of this variability are discussed and it is noted thatapparently identical plants, selected on a single morphologicalcriterion such as degree of elongation of the coleoptile, maybe expected to differ markedly in other morphological and anatomicalaspects, influencing their performance in physiological experimentation.