766 



BIOLOGICAL EFFECTS OF RADIATION 



and comparing their growth with that of plants similarly grown in the 

 open. With all the species he used, including beans, soy beans, begonias, 

 heliotrope, edelweiss, rye, oats, potatoes, and others, the plants were 

 tallest under the red glass, next tallest under Euphos glass, and shortest 

 in the open. In other words, they became the taller, the greater the 

 section of the spectrum that was cut off from them in the blue-violet 

 end. 



The following year, Schanz (38) gave an account of a more detailed 

 investigation in which his experimental plants were grown in eight beds, 

 each receiving a different kind of light. In the first five of these beds the 

 range of wave-lengths of light, transmitted by the screens used, was 

 gradually decreased from the ultra-violet end of the spectrum toward the 

 red. This enabled him to study more carefully the effect on plants of 

 light from which greater and greater regions of the spectrum were elim- 

 inated in the blue-violet end. In the last three beds he used combinations 

 of colored glasses which gave predominating colors of yellow, green, and 

 blue-violet, respectively. The characteristics of the screens used in the 

 beds are given in Table 1. 



Table 1. — Screens Used by Schanz 



Here again he found that the more the short rays were cut off from 

 the plants, the taller they became. Cucumbers, Fuchsia, chrysanthe- 

 mums. Lobelia, Begonia, and Oxalis gradually increased in height from 

 beds 1 to 5, reaching a maximum in red, and fell off in height gradually 

 from beds 6 to 8. Not all species responded in the same manner in beds 

 6 to 8. Potatoes and beets were weakest in yellow light (bed 6), a little 

 stronger in green light (bed 7), and still larger and healthier in blue- 

 violet light (bed 8). Leaves of Petunia were surprisingly large, those of 

 Oxalis esculenta, surprisingly small in the green light of bed 7. 



When plants were set out in the open from the different beds, the 

 time of flowering was hastened gradually, and the number of flowers and 

 fruits increased from beds 1 to 4. That is, the plants that had been grown 

 in the absence of all ultra-violet and some of the violet blossomed first 

 and produced the greatest number of flowers and fruit. In red, yellow. 



