These days of rockets and satellites are not only dangerous ones but also exciting ones. The information which has come pouring in about our atmosphere and the space around it from balloons, rockets, and satellites1,2 has emphasized the remarkable job the atmosphere does in protecting us from a number of space hazards. These studies also give many new insights into the action of high energy particles and of radiant energy on the atmosphere,1,3 of the effects of radiant energy on plants and animals,4 and the role of plants and animals in regulating the earth, the sea, and the atmosphere.5 This discussion is concerned with some special cases of the action of radiant energy on biological systems. Radiation Energy of the Sun About 93 million miles from Texas there is an average yellow star. It is about 100 times as bright as an average red star and