The structure and cytochemistry of the pistil of Hypericum calycinum: the stigma

Abstract

The pistil of Hypericum calycinum has a pentacarpellary, syncarpous ovary with five slender styles, each terminating in a small stigma. The stigma is dry and papillate with a thin lining of pellicle. The cuticle is thin and continuous around the papillae. A large vacuole filled with tannins occupies the major part of the papillae and the cytoplasm forms a thin lining around the vacuole. The cell wall of the mature papillae show two distinct layers-an outer layer of loosely woven fibrils and an inner denser layer with compact fibrils. A large number of small lipoidal bodies accumulate just below the cuticle. The papillae have fewer organelles than those typical of glandular cells. Dictyosomes observed occasionally are without associated vesicles. The cytoplasm is rich in ribosomes. The basal portions of the papillae merge into the transmitting tissue made up of loosely arranged cells. The intercellular matrix of the transmitting tissue is rich in lipids. Pollen grains are deposited between the papillae. Upon pollen germination, pollen tubes enter the stigma through the interstices between the papillae.