In some cases the plastid disappears and the crystalline pigment only is left.
The working of it is not at all completely understood at present, nor can we say exactly what is the part played by the pigment and what is the rfile of the protoplasm of the plastid.
6); and it has been suggested that the association of these two is analogous to the association of the rods and cones of the animal eye with their pigment layer, the light absorbed by the red pigment-spot setting up changes which react upon the refractive granule and being transmitted to the flagellum bring about those modifications in its vibrations by which the direction of movement of the organism is regulated.
In addition to its brilliance, vermilion is a pigment of great intensity and durability, remaining unaffected by acid fumes.
The absorption of these rays implies that the pigment absorbs radiant energy from the sun, and gives us some explanation of its power of constructing the carbohydrates which has been mentioned as the special work of the apparatus.