EFFECTS OF REGIONS OF VISIBLE SPECTRUM 11 Z 



shape of the curve falls off, shade plants showing a decrease at lower 

 mtensities than sun plants." Since the intensities in Popp's houses were 

 in the neighborhood of 50 per cent of full daylight intensity, it is likely 

 that greater intensities would have resulted in very little increased 

 dry weight. 



Shirley determmed the dry weights of plants grown in the houses 

 used by Popp but with only 10 per cent of the total daylight intensity 

 and with the substitution of a blue glass already mentioned, for the 

 window glass used by Popp, and Corex glass for G-86B. Under these 

 conditions he found that the entire spectrum (plants grown under Corex 

 glass) was more efficient for the production of dry matter than any 

 of the other qualities used. The lowest dry weights were uniformly 

 produced in the houses from which the blue-violet end of the spectrum was 

 eliminated. The blue end of the spectrum, according to his results, 

 was somewhat more efl&cient in dry weight production than was the red 

 end of the spectrum. 



MISCELLANEOUS PHYSIOLOGICAL EFFECTS OF DIFFERENT REGIONS OF 



THE SPECTRUM 



While it is likely that different regions of the visible spectrum may 

 affect differently the various physiological processes of the leaf, and of 

 the plant as a whole, very little accurate information on this subject 

 is available, except with regard to chlorophyll development and photo- 

 synthesis, both of which are considered elsewhere in this monograph. A 

 few remarks may be made concerning the effect of quality of light on 

 transpiration, stomatal movement, anthocyanin formation and absorp- 

 tion of inorganic substances. 



EFFECT OF DIFFERENT PARTS OF THE SPECTRUM ON TRANSPIRATION 



Since the rate of transpiration is so variable a quantity and is condi- 

 tioned by a whole series of interrelated internal and external factors, 

 many of which are beyond the control of the investigator, it is difficult 

 to obtain a knowledge of the effect of any one factor. Arriving at con- 

 clusions concerning the effect of light quality on transpiration is attended 

 with particular difficulty, since experiments with known light-quality 

 differences as the only variable or even the chief variable have been 

 rare. 



The literature on the subject is not voluminous. It is assembled and 

 summarized, although perhaps not entirely properly evaluated, in the 

 monograph of Burgerstein (5). Sachs in his lectures on plant physiology 

 and in the second English edition of his textbook considers the status 

 of the problem up to his time. The conclusion reached by Sachs, that 

 we are still in doubt as to whether radiation as such, independently of 

 the higher temperature caused by it, influences transpiration, is still 



