ULTRA-VIOLET AND SEED PLANTS 863 



INVESTIGATIONS DEALING WITH PLANTS GROWN IN DAYLIGHT FROM WHICH 

 THE ULTRA-VIOLET PORTION WAS REMOVED 



Schanz (89) concluded that the eUmination of the ultra-violet was 

 beneficial to plants and recommended Euphos glass, which excludes 

 ultra-violet, for greenhouses. His failure to take into consideration light- 

 intensity differences makes it doubtful whether his results were really 

 quality effects. 



Popp (71) in 1925 conducted experiments at the Boyce Thompson 

 Institute. Here for the first time seed plants were grown in light of 

 various ranges of wave-lengths under controlled and stated conditions, 

 particularly with regard to light intensity and quality. When only 

 the ultra-violet portion of solar radiation was removed by a No viol "0" 

 screen of the Corning Glass Works without reducing the total intensity 

 of the radiation over that of the controls, no significant effects were pro- 

 duced on plants as evidenced by general appearance, development of 

 pigments, rate of growth, time and amount of flowering and fruiting, 

 fresh and dry weights, amount of total carbohydrates, starch content, 

 total and soluble nitrogen, and some of the higher organic compounds. 

 Any indications given were in favor of the elimination of the ultra-violet. 

 If, however, the blue end of the visible spectrum was removed with the 

 ultra-violet, then decidedly abnormal plants resulted. 



The experiments of Shirley (102) have indicated that the blue- 

 violet end of the solar spectrum is more efficient in dry-weight production 

 than the red end, when light intensities are uniformly 10 per cent of 

 that outside. The removal of the ultra-violet and of some violet, how- 

 ever, caused no very significant decrease in efficiency, which is to be 

 expected when we consider the small percentage of total radiation in 

 this region. 



Jacobi (40) attempted to determine whether the formative effects 

 of ultra-violet radiation such as dwarfing, hairiness, thicker and smaller 

 leaves, brighter colored flowers, etc, as claimed by Schanz (88), were 

 really ultra-violet effects or whether they were light-intensity effects. 

 He grew plants under Uviol, an ultra-violet transmitting glass, and 

 Euphos, an ultra-violet absorbing glass, under solar radiation, and then 

 sought to confirm his results as quality effects by performing laboratory 

 experiments with artificial illumination in which an attempt was made 

 to equalize intensities. He concluded with Schanz that the dwarfing 

 effects were quaUty effects caused by ultra-violet radiation. He went 

 still further and determined fresh and dry weights of his laboratory 

 plants. Fresh weights came out in favor of Euphos glass, and dry weights 

 in favor of Uviol glass, which was thought to be an indication that ultra- 

 violet favors dry-weight production. However, the fact that fresh 

 weights came out in favor of the Euphos glass, is an indication that one 



