THE ULTRASTRUCTURE OF POLLEN-GRAIN DEVELOPMENT IN THE OLIVE (OLEA EUROPAEA). 1. PROTEINS IN THE PORE*

Summary The olive tapetum is of the parietal type and the walk of the tapetal cells disappear at about the time as the microspore tetrads separate. As the intine starts to develop in the microspore the Golgi bodies are apparently active in discharging vesicles, and fibrillar PAS-positive material starts to accumulate between an undulant plasmalemma and the intine. The plasmalemma then retracts from the pore zone and within the crescent-shaped area thus formed accumulates what is believed to be a pectocellulosic wall much penetrated by invaginating tubules from the plasmalemma. After the first haploid mitosis more material forms between the plasmalemma and the pore apparently sealing off these invaginations. Fibrillar material thought to be protein first appears in the intercellular spaces between the tapetal cells and finally becomes concentrated over the outer surface of the pollen pore. This proteinaceous material does not accumulate if the cytoplasm of the pollen has degenerated prior to pore formation.