Untersuchungen über die Biotechnik der Apocynaceenblüte : I. Morphologie und Funktion des Narbenkopfes

Abstract

The paper deals with the results of morphological, ultrastructural and biochemical investigations on the apex of style of the Apocynaceae . The organ is formed by the postgenitally fused tissue of carpel tips. Two types of style apexes can be discerned: the Plumeria -type and the AllamandaNerium -type. The latter exerts a higher degree of differentiation and can be subdivided into apical appendages, cylindric part, hairwreathes, collar and basal, circular depression. Analogous to the morphological differentiation a functional division occours in auxiliary structures and in the stigma proper. The glandular epithelium, located on the cylindric part, produces an adhesive with the help of which pollen grains are glued to the mouth parts of insects. The adhesive-producing glands have lost their original stigmatic properties; the receptive area is reduced to the circular stigmatic depression at the bottom of the apex of style. The locality of the stigma has been confirmed by experiments. As the main constituents of the previously unknown adhesive secretion, terpenoids and a polysaccharid have been established. Cuticles of cutin-derivatives enclose bubble-like areas of “secretion chambers” into which the adhesive is secreted in a granulocrine way. It is assumend that the polysaccharide, consisting of arabinose and galactose, is formed by the Golgi apparatus. The connections of Apocynaceae to the Asclepiadaceae are discussed with regard to the style, morphology and function. The adhesive of Apocynaceae and the translators of the Asclepiadaceae are homologous products, a conclusion which agrees with their ultrastructure and biochemical composition.