Light reaction in lower organisms. II. Volvox globator

Light Antennas in phototactic algae.

“…Mutants with incorrectly oriented antennas cannot track (122). The coenobium is densest in the rear, where there are large reproductive cells and autocolonies (171,215). Because of this asymmetry, motile colonies swim upward in the dark, and nonmotile colonies sink with the posterior end downward (171,215).…”

The Vertical Distribution of Volvox in the Plankton of Lake Monona

“…We know from the studies of Marshall Ward (3) and others that direct sunlight kills many algae. Mast (5) has shown that this is also true for Volvox. Since the colonies were in full sunlight on the 7th, it is not at all improbable that they were killed by this strong light and gradually sank to the bottom.…”

“…Geotaxis, however, plays an important part in the distribution of Volvox. Mast (5) finds that, when a horizontal beam of light is thrown across an aquarium, the colonies tend to move horizontally towards the source of light, but the force of gravity pulls them downwards so that they sink very rapidly until, as a result of the difference in weight between the anterior and posterior ends, they become vertically oriented and begin to swim upwards. He also finds that after an aquarium has been in darkness some four or five hours many colonies are at the surface of the water.…”

“…The physiological condition of the colony affects this upward swimming. Mast (5) observed that the colonies would be lying motionless on the bottom of the aquarium after standing in darkness for some hours. When illuminated they did not respond immediately, but after a while slowly began to move in all directions, later becoming normally active and moving towards the light.…”

“…Light is by far the most important factor governing the distribution of Volvox. The response to light by Volvox has been noted by many naturalists, but Oltmanns (7), Holmes (2) and Mast (5,6) are the only ones to have made quantitative studies. Oltmanns produces a graded intensity in the illumination of an aquarium by passing a beam of light through a hollow glass prism filled with a mixture of India ink and gelatine.…”