This paper proposes a new interpretation for primary thickening in monocotyledons. The anatomy of the vegetative organs of the following species was examined: Cephalostemon riedelianus (Rapataceae), Cyperus papyrus (Cyperaceae), Lagenocarpus rigidus, L. junciformis (Cyperaceae), Echinodorus paniculatus (Alismataceae) and Zingiber officinale (Zingiberaceae). The endodermis with meristematic activity was observed in the root of all the species, in the stem of Cyperus, Cephalostemum and Lagenocarpus rigidus, and in the leaf trace of Cyperus and leaf of Echinodorus. Considering the continuity of tissues through the root, stem and leaf, the authors conclude that in the stem the pericycle remains active throughout the life of the plant as the generator of the vascular tissue. The "Primary Thickening Meristem" is in fact the pericycle plus the endodermis and its derivatives (or only the pericycle). Close to the stem apex, the assemblage of seems to be a unique meristem, giving rise to the inner cortex and vascular tissues.

Fully developed leaves of Cryptochloa capillata (Swallen) Soderstrom, Raddia brasilienses Bertol and Pharus lappulaceus Aublet (Poaceae: Bambusoideae) were collected at Restinga de Jacarepiá, Environment Proctection Area of Massambaba, county of Rio de Janeiro, State of Rio de Janeiro, Brazil, and studied by optical microscope. Leaf anatomy is described in order to contribute to the Poaceae family study. Anatomic features observed in the three studied species such as: midrib with complex vascular system, mesophyll consisting of tabular lobed chlorophyllous elements and fusoid cells, vascular bundles with double sheath, epidermis made up of long cells, short cells, micro-hairs, prickles and silica bodies correspond to the "bambusoid type" of leaf anatomy.

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RESUMO O presente trabalho aborda a anatomia foliar de Blutaparon portulacoides (A. St.-Hil.) Mears. (Amaranthaceae), Ipomoea pes-caprae (L.) R. Br. e I. imperati (Vahl) Griseb. (Convolvulaceae), Canavalia rosea (Sw.) DC. e Sophora tomentosa L. (Leguminosae), Sporobolus virginicus (L.) Kunth (Poaceae) e Miegia maritima (Aubl.) Willd. (Cyperaceae). A maioria das espécies investigadas tem folhas suculentas e epiderme uniestratificada coberta por espessa camada cuticular. A densidade de tricomas apresenta-se distinta entre as espécies. Os estômatos ocorrem em uma ou ambas as faces da folha estando as células estomáticas situadas ao mesmo nível ou ligeiramente abaixo das demais. Tecidos aquíferos foram observados em todas as espécies estudadas, assim como cristais, fibras e estruturas secretoras. A estrutura do mesofilo varia entre as espécies, sendo dorsiventral, isobilateral ou Kranz. Em todas as espécies estudadas foram identificados caracteres xeromorfos.

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