The Dark Fixation of Carbon Dioxide as a Factor in Photoperiodism

and the latter especially gives an almost perfect single recessive ratio when grown in the field. This paper deals primarily with the white mutant. Extensive tests show this white strain to be devoid of carotenoids, but nevertheless it is a vigorous seedling, grafts freely, and as a scion sets seed to its own pollen. The seedling reacts to gravity and light, and under suitable conditions produces one-half to two-thirds as much protochlorophyll, chlorophyll a and chlorophyll b, as do seedlings of its green sib under like conditions. The ratios of these three pigments is stable over a wide range of conditions. A wide range of studies on light intensities and exposure time show maximum pigment production writhin 72 hours at 0.5 fc of light. Protochlorophyll is formed in both light and darkness, but varies somewhat with the age of the seedlings. Long exposures from 2 to 16 hours to light intensities of 250 to 2000 fc cause severe fading. Preliminary tests show that if dark-grown seedlings are exposed to sufficiently strong light, their capacity to produce chlorophyll is destroyed.