Morphological Study of Agave lechuguilla

Abstract

1. Origin of the floral organs of Agave lechuguilla is acropetal, sepals appearing first and carpels last. 2. The flower is epigynous. Its vascular anatomy is simple, being a direct divergence of vascular bundles into the separate organs. All vascular bundles ending in either sepal or petal structures are derived from bundles differentiated early in connection with these floral parts. 3. The ovule is anatropous and has two integuments. Placentation is axial. 4. Megasporogenesis starts with differentiation of a single hypodermal archesporial cell and ends with formation of a tetrad of megaspores arranged usually in linear fashion. Two variations in megaspore arrangement were noted. 5. Periclinal division of the archesporial cell gives rise to a primary parietal cell and to a single primary sporogenous cell which enlarges and becomes the megaspore mother cell. Development of the megagametophyte follows the so-called normal type. 6. A single parietal layer is present in the ovule, disintegrating when the megagametophyte enlarges. 7. The vascular tissue of the ovule does not stop at the base of the chalaza but tracheids penetrate the nucellus to the megagametophyte. 8. Anther development follows the common method. The archesporium consists of a group of cells. Periclinal divisions give rise to the primary parietal and primary sporogenous cells. Continued periclinal and anticlinal divisions of the primary parietal cells form the wall tissue. The sporogenous cells enlarge and function as microspore mother cells. There are two successive divisions of the microspore mother cells, resulting in four microspores. 9. The tapetum is derived from the innermost layer of the parietal tissue. 10. The mature anther shows well-defined endothecia three or four cells in thickness and disintegration of the stomium.