Fine Structure of Capitular Filaments in the Coenocytic Green Algapenicillus1,2,3

SUMMARY Capitular filaments ofPenicillus capitatuscontain a large central vacuole. The parietal cytoplasm is densely packed, devoid of chloroplasts in the growing tip, and becomes convoluted and sponge‐like as extensions of the vacuole penetrate the cytoplasm in mature portions of the filament. Structure of organelles and their distribution in the filament are described. The vacuole contains a variety of inclusions, such as membranous configurations, spherical bodies, electron dense bodies, and calcium oxalate monohydrate crystals, each of the latter surrounded by a chamber associated with microtubules. Endophytic bacteria are present throughout the vacuole and occasionally in the tip cytoplasm. Some vacuolar components ofP. pyriformisare described for comparison.