778 BIOLOGICAL EFFECTS OF RADIATION 



Schanz (38) observed that flowers became paler in color the more 

 the blue-violet end of the spectrum was reduced. Best flower color, where 

 this color was caused by anthocyanin, always occurred in the open. In 

 leaves in which there is an epidermal layer of anthocyanin, as in a 

 reddish-colored lettuce, anthocyanin development was somewhat checked 

 under window glass and failed to develop altogether when wave-lengths 

 shorter than 3800 A were ehminated. In his beds 3 to 8, inclusive, this 

 lettuce became fully green. Red beets showed a somewhat similar effect, 

 but the petioles remained red in all beds. Begonia leaves became fully 

 green in beds 4 to 8. When any of these plants were transplanted to 

 the open, they immediately developed anthocyanin. From this Schanz 

 concluded that ultra-violet radiation was necessary for the development 

 of anthocyanin in such plants. In Popp's (34) work the greatest reduc- 

 tion in anthocyanin development occurred when not only the ultra-violet, 

 but also the violet and the blue were eliminated. From the fact that some 

 plants develop anthocyanin in the dark, it is obvious that light is not 

 absolutely necessary for its formation, yet it probably does influence the 

 intensity of its development. More accurate work will have to be done 

 before this question can be settled. 



A number of workers have used different types of radiation to develop 

 the anthocyanin color in the skin of apples. Pearce and Streeter (29) 

 found that with sunlight as a source, wave-lengths between 3600 and 

 4500 A with an optimum at 4100 A, were the most effective portion 

 of the spectrum during October and November for coloring Mcintosh 

 apples. Arthur (1), on the other hand, using various filters and a mer- 

 cury-vapor arc source, found that in addition to ultra-violet between 

 wave-lengths 3120 and 2900 A, all of the visible up to 6000 A was effective 

 in reddening Mcintosh apples. Other workers have reported ultra- 

 violet radiation to be the most effective. 



A more detailed discussion of the relation of radiation to anthocyanin 

 formation is given by Arthur (Paper XXV) in this monograph. 



QUALITY OF LIGHT AND ABSORPTION OF INORGANIC SALTS 



That different portions of the visible spectrum affect differently the 

 absorption of inorganic salts by higher plants has been advanced by 

 several investigators. 



Nemec and Gracanin (27) report that violet and red Ught have little 

 effect on the absorption of phosphoric acid, but markedly increase the 

 absorption of K2O during the first 18 days of the growth of rye plants. 

 The plants were grown under various colored glasses and under clear 

 glass. 



Tottingham et al. (49) found that increasing the proportion of radia- 

 tion in the blue end of the spectrum above that emitted by a Mazda 



