Carotenoids are present in the thylakoid membranes of higher plants, algae, and photosynthetic bacteria; one part of their function is to serve with lesser or greater efficiency as accessory pigments for light-harvesting in photosynthesis. Many of the vividly red, orange, or yellow flowers and fruits, as well as a number of animals, owe their appearance to the presence of a class of more-or-less unsaturated tetra-terpenoids called “carotenoids”. Carotenoids, once extracted, are labile and require protection from heat, light, and oxygen. In a centrifuge tube, the carotenoid to be crystallized is dissolved and hot methanol is added to begin crystallization. Carotenoids should not be exposed to bright light; the laboratory windows should not face the sun, and vessels, chromatography columns, and Thin-layer chromatography tanks should be covered with black cloth, aluminum foil, etc., where appropriate. Chromatography should be carried out in the dark, but nonitrogen atmosphere is required.