THE ROTATED-LAMINA SYNDROME .3. CASES IN BEGONIA, CORYLUS, MAGNOLIA, PELLIONIA, PRUNUS, AND TILIA

The rotated-lamina syndrome occurs in all adult shoots of Tilia x euro paea, and in lateral shoots of Corylus spp. and Prunus laurocerasus. C orylus and Prunus also have orthotropic radially symmetrical shoots th at have normal leaf orientation. Development of the syndrome in leaf p rimordia in Tilia and Corylus is similar to that previously described in Ulmus, i.e., the leaf primordium is initially asymmetrical so that the leaf blade component of the primordium arises facing only obliquel y towards the shoot apex, and further asymmetrical outgrowth of the le af buttress brings the leaf blade region into the rotated position. Le aves of Begonia foliosa and the ventral leaves of (anisophyllous) Pell ionia pulchra arise from initially symmetrical primordia, and lamina r otation occurs by asymmetric growth at the base of die leaf blade regi on. The process is similar to that in the woody examples but occurs at a proportionately later stage of leaf development. Development of the syndrome in Prunis laurocerasus and Magnolia x soulangeana differs co nsiderably. Primordia are slightly asymmetrical but have normal dorsiv entrality at first, but when the lamina arises the two edges of the le af blade grow towards the same (upper) side of the bud, and this is re sponsible for most of the appearance of rotation. In general the upper stipule is initially larger than the lower and arises much earlier in Corylus and Tilia. Leaves that have normal orientation in Corylus and Prunus develop from quite symmetrical primordia, but those of Corylus may show some asymmetry of stipule development. Shoots of all cases c an be considered to show heteroblastic growth, and the early part of t he heteroblastic sequence is prolonged in the orthotropic shoots with normally oriented leaves in Corylus and Prunus. The morphological and morphogenetic significance of the rotated-lamina syndrome is discussed .