RADIATION AND ANTHOCYANIN PIGMENTS 1113 



favor pigment formation. The author observed that the scales withered 

 rapidly in the open sunlight. 



TEMPERATURE, RADIATION, AND ANTHOCYANIN FORMATION 



Anthocyanin pigments in nature develop best in the spring and 

 autumn when temperatures are lowest. Overton (26) found that the 

 higher the temperature the less pigment was formed in Hydrocharis 

 leaves. Klebs (17) also observed that flowers of Primula sinensis and 

 Campanula trochelium were more highly colored when grown in the cold. 

 Bonnier (7) and Heckel (15) have noted the increased pigmentation of 

 flowers grown at high altitudes as compared with those grown in low- 

 lands. Many workers have discounted the possible direct effect of low 

 temperatures on anthocyanin formation, preferring to believe that the 

 effect is due to the accumulation of the products of photosynthesis, 

 especially sugars, at low temperatures. In the case of autumnal coloring 

 of leaves it has been pointed out above that no definite proof of such an 

 accumulation exists in the period during which color develops. The 

 evidence here is largely in favor of a low temperature effect on pigment 

 production or of other factors not yet studied thoroughly. Kosaka (18) 

 has studied recently the effect of both low temperature and light intensity 

 on pigment development in chrysanthemum flowers. The pigment 

 was developed only in light. Using shading cloth he determined that 

 lower light intensities produced less color. Low temperatures of 7° to 

 15°C. favored, while higher temperatures of 25° to 30°C. inhibited, 

 pigment development. 



Many fruits develop red color only in light. In others pigment 

 production is aided by exposure to light. Fletcher (13) found that when 

 growing apples were bagged while on the tree in red cellophane bags 

 which had a low transmission in the blue region, red pigment failed to 

 develop. If the fruit was bagged late in the growing season, color 

 developed more rapidly than in nontreated fruit when the bag was 

 removed at maturity and the fruit exposed to sunlight. Schrader and 

 Marth (31) found that a single layer of muslin greatly reduced pigment 

 formation in five varieties of red apples, while two layers almost com- 

 pletely prevented pigment formation. The transmission of the cloth 

 as measured with a Weston photronic-cell photometer was 61.4 per cent 

 for one layer and 39.2 per cent for two layers. 



Recent studies have shown that red pigment may be developed in 

 certain varieties of apples after these have been detached from the tree. 

 Magness (20) found that Jonathan apples were colored by exposures of 

 1 hr. each day to "dilute ultra-violet fight." Greater exposures injured 

 the fruit. He also observed that fruit did not color so rapidly when 

 exposed to sunlight through window glass as when exposed directly. 

 Holding the fruit in storage for two weeks retarded pigment develop- 



