Anatomy of the Axis of the Banana

Abstract

Musa sapientum was studied on plantations in Central Amer. Each branch of the rhizome arises from a bud of unusual position and swells into a massive bulbous organ. Behind the growing point of this "bulb" is a bundle-forming meristem of limited activity. Each meristem cell forms at most about 7 tangential divisions, and is then replaced by a cell of the inner cortex. At about 5 mm. from the apex the procambium is recognizable and produces longitudinal bundles; at 25 mm. from the apex it originates transverse bundles; at 35 mm. it disappears. Adventive roots arise in longitudinal rows of 4 and push outward through cortical tissue softened by enzymatic action, but there is no digestive pocket. The secondary bundles connect the roots with the leaf-traces and are amphiphloic, while all other bundles of the shoot are collateral. The courses of the vascular bundles were determined by staining and then dissecting; 5 types were recognized. The amphiphloic longitudinal secondary bundles are the direct downward prolongation of the collateral leaf-trace bundles. A method of determining the lengths of the tracheids was devised; some 8 cm. long were found in both the aerial stem and the leaf-sheaths. The latex vessels consist of chains of cells joined by a wide perforation occupying almost the entire end wall. The central portion of this wall is torn bodily away from a narrow peripheral zone, but usually remains attached at one side, forming a loose flap.