Morphological and anatomical structure of Campanula latifolia L. fruits

Abstract

The inner fruit structure in Campanula latifolia L. was studied using light microscopic technique. Our aim was to revise the dehiscenсe mode in the fruit and find out from which part of ovary the axicorn – peculiar organ inside ovary, is formed and which tissues it contains. The fruit of C. latifolia has a persistent central column with three septa attached. We showd that during fruit ripening, three dips appear in the lower fruit part, followed by formation of a hippocrepiform slit at the lower margin of each dip, providing an opening. The valves that cover each opening bend outwards. Exocarpium is composed of one-cell layer with non-lignified walls. Mesocarpium is multilayered, mostly parenchymatous, with numerous vascular bundles. Endocarpium is uniseriate, non-lignified, composed of small flattened cells. Vascular system of the fruit wall is composed of 10–12 large concentric vascular bundles with annular xylem organized in a single ring. In the lower part of the ovary, the inner cell layers of the mesocarpium as well as parenchyma of septas become lignified. This lignified tissue contains isodiametric and polygonal cells with thick walls. Before the fruit wall opens, it is visible that septa detach from a central column just on the boundary between lignified and non-lignified parenchyma. On the longitudinal sections, lignified parenchyma has a form of vertical band extending from the base to the top of the ovary. This vertical band of tissue differentiating early during the fruit development and being well-distinguished from the adjacent parenchyma is the axicorn. In C. latifolia, it has a complex, mattock-like shape. The lower margin of axicorn causes formation of the hippocrepiform opening in the ovary wall. Our investigation provides an evidence that the axicorn is not an organ sui generis inside the ovary of Campanula, but it is merely a band of lignified parenchyma of the mesocarpium and especially of septa which is commonly found also in other members of Campanulaceae. The fruit of C. latifolia is considered to be an inferior trilocular capsule with septifragal-hippocrepiform dehiscence.

Keywords

• giant bellflower
• inferior capsule
• fruit wall
• septifragal dehiscence
• hippocrepiform slit
• axicorn