LARSON, P. R. 198.5. Rachis vascularization and leaflet venation in devclopiny leaves of Frcrsinu.spenn.sy/vnnica. Can. J . Bot. 63: 2383-2392. Leaves of Fraxi~l~i.spent~.sylvnt~ica are sewcd by a double tracc that exits thc stcm vasculature through a single gap. During embryonic leaf dcvclopment, the leaf traces subdivide in the nodc to produce subsidiary bundlcs that differentiate acropetally in the leaf base and basipetally in the stem. The acropetal bundles converge distally in the node to form a rachis vasculature consisting of a semicircular arc joined by a ventral chord. Each lateral leaflet is vascularizcd by bundles contributed by both the semicircular arc and the ventral chord of thc rachis. Onc rachis ridge bundle divides to form two leaflet ridge bundles and a new rachis ridgc bundle diverges from thc ventral chord. Thc lcaflct ridge bundlcs diverge as basal vcins and subsequent secondary veins diverge from the midvein in an approximate right-left scqucnce. Grecn ash has odd pinnate leaves; the terminal leaflet is vascularized by the rachis residual following departure of thc last leaflet pair. Secondary vcins extcnd to the lamina margins and then curvc upward to initiate thc marginal loops of the brochidodromous venation. Periclinal divisions occur in close association with secondary vcins in the prospective platc meristem region. Anticlinal divisions occur in subepidermal layers of the internal ridge points in the prospectivc palisade mesophyll rcgion.The lattcr divisions probably contribute both to lamina extension and to spreading of the conduplicatcly folded lamina wings. LARSON, P. R. 198.5. Rachis vascularization and lcaflct venation in developing leavcs of Frcrxinus pe~~n.sylvc:r~ica. Can. J . Bot. 63: 2383-2392. Les feuilles du Frclxinus pennsylvar~icn comportent unc double tracc foliairc qui les relie au systeme vasculaire de la tige par une breche foliaire simple. Au cours du dCveloppcment de la fcuillc, les traces foliaires se subdiviscnt dans le noeud pour produire des faisceaux subsidiaires qui sc diffkrencient en direction acropitte dans la base de la feuille et de faqon basipete dans la tige. Les faisceaux acropetes convergent distalement dans le nocud pour former unc vascularisation en rachis lequel consiste cn un arc semicirculaire reliC par un cordon ventral. Chaque foliole IatCral cst vascularis6 par des faisceaux issus a la fois de I'arc semicirculaire et du cordon ventral du rachis. Un faisceau de la crCtc du rachis se subdivise pour former deux faisceaux de la crCte des folioles, et un novueau faisceau de la crCte du rachis diverge du cordon ventral. Les faisceaux de la cr&te du rachis des folioles divergent et formcnt les nervures basales, et Ics ncrvures secondaires subskquentes divergent de la nervure centrale dans unc sCquence j. peu pres gauche-droite. Le fritne de Pcnnsylvanie possede des feuillcs pennCes impaircs; le foliole terminal est vascularisC par les rCsidus du rachis suite au ddpart de la dernierc pairc de folioles. Les nervures sccondaires s'Ctcndent jusqu'aux m...