Pollen, pistil and their interrelations in Borago officinalis and Heliotropium europaeum (Boraginaceae)

The pollen grains, the pistil, growth of the pollen tube and its pathway are described in Borago officinalis and Heliotropium europaeum. The exine is thick in both taxa but it is covered with dense gemmae in Borago. The intine seems to be thicker and contains more proteins in Borago than in Heliotropium. Starch is very abundant in the latter while it is lacking in the former. The style is hollow in Borago with a stylar canal running from the stigma to the ovary, while in Heliotropium it is broadly cone‐shaped with papillae located at the base of the cone (the “stigmatic ring") and not at the top of the style as usual. In Borago stigmatic papillae are unicellular, skittle‐shaped and have a thick pectocellulosic wall and an equally thick cuticular layer, while in Heliotropium the stigmatic papillae are unicellular, elongated cone‐shaped with a thin pecto‐cellulosic wall and have an apparently reduced cuticular layer. The stigmatic exudate is very abundant on the stigmas of Heliotropium even before anthesis while it is absent on those of Borago except when allo‐pollination occurs. Pollen tube growth has been followed from stigma to ovules in both taxa.