EFFECTS OF REGIONS OF VISIBLE SPECTRUM 769 



Under those conditions the bhie-violet end of the spectrum proved to be 

 somewhat more efficient in dry-weight production of plants than the red 

 end, but not nearly so efficient as the full spectrum under the same total 

 intensity. The plants in the blue house were somewhat stunted, having 

 very short internodes, but sturdy stems. The blue end of the spectrum, 

 therefore, seemed to be more efficient in producing a plant of normal 

 stature and growth than did the red end, when only 10 per cent of the 

 total intensity of daylight was transmitted by each. What would happen 

 if plants could be supplied with light consisting exclusively of the blue- 

 violet end of the spectrum at an intensity comparable to that of daylight 

 has never been determined. At the present time no satisfactory method 

 is available for attacking this problem. 



Shirley (43) also grew plants under approximately the same conditions 

 Popp used and arrived at practically the same results. 



Pfeiffer (31) studied anatomically stems and leaves of plants grown in 

 the different houses used by Popp and Shirley. Unfortunately, the 

 intensities of radiation were not equalized in the different houses and 

 hence, except for the two houses in which intensities were about the same, 

 namely, the one covered with Noviol "O" which eliminates only ultra- 

 violet, and the full-spectrum house, there is no way of differentiating in 

 her work, as she herself points out, between intensity effects and quality 

 effects. She did, however, find the same lack of differentiation of tissues 

 and weaker development of stem and leaf tissues when the blue-violet 

 end of the spectrum was eliminated, as has been mentioned previously. 

 Vascular development was always best in the full spectrum. When only 

 ultra-violet radiation was eliminated, stems and leaves of four-o'clocks, 

 sunflowers, and soy beans were somewhat thinner, and perhaps somewhat 

 weaker in vascular development. 



Teodoresco (47) also states that plants developing under red-orange 

 light show a growth comparable to that in darkness, while plants exposed 

 to blue-violet light resemble those developed in white light, even though 

 grown under lower total intensities. Blue light, according to him, retards 

 growth in length of stems and petioles but favors growth in surface and in 

 thickness of leaves. An exception to this was found in Menispermum 

 Cocculus, the petioles of which were shorter in red light and in darkness 

 than in blue light or white light. He also found that more internodes are 

 developed in red light and in darkness than in blue light or white light. 

 In general, his results on the higher plants agree with those of Popp and 

 Shirley. Much of his work was with Bryophytes and is therefore outside 

 the scope of this review. 



Funke (13) has also published a rather extensive paper on the effect of 

 light of different wave-lengths on the growth of plants. He worked 

 chiefly with water plants and moor plants. While, after a fashion, he 

 does give the transmissions of the screens he used (gray, red, green, and 



