Achlya recurva. Cultures were placed in darkness and in diffuse daylight on top of a laboratory table at approximately the same temperature. They were examined after 72 hours. Dark cultures were then left in daylight for an additional 72 hours. Light was necessary for the germination of zygotes. (Ziegler, A. W. , 1948). Albugo occidentalis. Hanging-drop slides of conidia were arranged in a chamber at 12°C so that light from a 3-cell flashlight fell on them, while others were placed in the dark. Results after 48 hours showed that spores germinated equally well in light or darkness, (Raabe, R. D,, and G. S. Pound, 1952). Allomyces arbuscula. Cultures exposed to darkness for 7 days and to diurnal illumination for the same period formed zones under both conditions. (Hatch, W. R, , 1936). Blakeslea trispora. Sporangia formed profusely in bright light, subdued light, and total darkness. The shortest sporangiophores were produced in bright light. During their development the sporangiophores were distinctly phototropic. (Weber, G, F. , and F, A, Wolf, 1927). Blastocladiella emersonii. A normal strain and a carotenoid-bearing mutant grew more rapidly in light than in darkness. Illumination induced an increase in CO2 fixation and concomitantly a large increase in the labeled succinate and a decrease in the labeled ketoglutarate pools in the organism. Both labeled and unlabeled glucose were consumed more rapidly in the light than in the dark. Cell-free preparations mediated an enzymatic TPN-dependent oxidation of isocitrate which was inhibited by bicarbonate and light. These same preparations mediated an enzymatic oxidation of reduced TPN which was accelerated by ketoglutarate and bicarbonate; simultaneously, ketoglutarate was carboxylated. These reactions were further accelerated by light. The mechanism of the effect of illumination was tentatively interpreted in terms of a lightstimulated cyclic process, the S.K.I, cycle. This involved carboxylation of ketoglutarate, via isocitric dehydrogenase and perhaps citritase, to succinate and oxalate, and the further carboxylation of some of the succinate to yield ketoglutarate once again. (Cantino, E. C. , and E. A. Horenstein, 1956). Blastocladiella emersonii. Submerged, liquid cultures proliferated more rapidly and produced greater yields of plant material in white light than in darkness. Illuminated, growing cultures of orange plants grew more rapidly in bicarbonate media and fixed more CO2 per unit weight of organism produced, than those incubated in darkness. The quantity of light necessary to induce the effect was not high. The degree of stimulation rose linearly with increasing intensity to about 100 f. c. which yielded maximum results; further increase in intensity up to 300 f. c. neither stimulated nor inhibited. The effective spectrum was in the range of 400-500 m^.