MONOCHROMATIC LIGHT CURVES 1167 



utilization of light energy," and also to determine the reaction of photo- 

 synthesis to changes in temperature. In another paper, Danilov (1938) 

 concluded that the effect of various colors of light on photosynthesis depends 

 on the method of cultivation of the algae. In particular, variations in the 

 sensitivity to different colors of light were caused by changes in hydration 

 of the cells (achieved by culturing Scenedesmus in 1% sodium chloride solu- 

 tion). 



Ursprung (1917, 19182), working with detached leaves by means of Timiriazev's 

 (1890, 1903) "starch spectrum" method (a spectrum is projected on a starved, destarched 

 leaf, and the "latent starch image" formed by light is "developed" by iodine), found, 

 in light of uniform spectral intensity, a continuous decrease in the production of starch 

 from red to violet, without a second maximum, and attributed this result to the closure 

 of the stomata and consequent quenching of photosynthesis in blue-violet light. 



Dastur and Samant (1933), Dastur and Mehta (1935) and Dastur and 

 Solomon (1937) described observations that purported to show that pure 

 red light (or pure blue light) is less efficient in photosynthesis than a com- 

 bination of both. Their experiments were criticized by Montfort (1937), 

 who found that the addition of blue-violet light to red light has no effect 

 on the rate of photosynthesis, provided the red light was in itself of saturat- 

 ing intensity (this agrees with the experiments of Button and Manning 

 with diatoms, described on page 1172). 



Dastur, Kanitkar and Rao (1938) measured the formation of proteins 

 in leaves in light of different color, and found differences which they related 

 to the above-mentioned observations on photosynthesis in colored light. 



The results of Dastur and co-workers probably are trivial, being caused 

 by the use of optically dense tissues. As explained above, such tissues 

 must (and do) utilize moderately intense green or yellow light better than 

 orange-red (or blue-violet) light of the same intensity, because the latter 

 is absorbed in too thin a layer and causes saturation effects there. White 

 light of partly saturating intensity, since it contains green and yellow, will 

 give, in such tissues, a higher yield of photosj^nthesis than an equally strong 

 red-orange or blue-violet light. 



The hypothesis of Baly (1935) that photosynthesis requires a quantum of red plus 

 a quantum of blue light, was mentioned before (Vol. I, p. 554) and characterized as 

 entirely without experimental basis. 



In chapter 28 (page 987) we described the different shape of light curves 

 of shade-adapted and light-adapted plants. Since these plants differ in the 

 composition of their pigment systems, they are likely to show differences 

 also in their response to light of different color. Lubimenko (1923) ob- 

 served that shade-adapted plants often are relatively more efficient in blue- 

 violet light (and relatively easily inhibited by red light). This may be as- 



