1026 



BIOLOGICAL EFFECTS OF RADIATION 



obtained by Seybold (104a) for determinations of the absorption of 

 10 species of white and green leaves. The wave-lengths of light given 

 represent maximum transmission of the filters used. The results were 

 in general confirmed by Seybold (104c) with the use of a monochromator 



(Fig. 2). 



Table 2. — Percentage Transmission, Reflection, and Absorption of Light, 

 Mean Values of 10 Species of Leaves Obtained by Seybold 



Wave-length, ni/u 



Transmission 



Reflection 



Absorption 



Absorption coefficients. 



White-leaf lamina 



644 

 33 

 46 

 21 



578 

 33 

 47 

 20 



509 

 31 

 43 

 26 



436 

 20 

 27 

 53 



336 



8 

 18 

 74 



0.21 0.20 0.26 0.53 0.74 



I 



Green-leaf lamina 



644 578 509 436 336 



9 10 10 2 



13 14 14 11 9 



78 76 76 87 91 



0.78 0.76 0.76 0.87 0.91 



The green leaves of Pelargonium zonule, on the basis of energy meas- 



o 



urements, show two absorption maxima: at X6700 A and at 4800 to 



o o 



4100 A and two absorption minima: at X7300 and 5400 A. Little is 

 known regarding either absorption or reflection in wave-lengths longer 



o o 



than X7400 A and shorter than 4100 A. The absorption at the maxima is 

 about 90 per cent of the incident light, and for the minima it is about 

 60 per cent at X7300 A and 74 per cent at X5400 A. 



The main absorption by the leaf must, of course, be ascribed to the 

 pigments and this amounts to about 60 to 70 per cent, so that the distribu- 

 tion of energy can, according to Seybold, be placed as follows: 



Per Cent 



Incident energy 100 



Absorption of the colorless leaf substance 10 



Reflection 10 



Transmission 10 



Absorption by the chloroplasts 70 



Determinations with pigmented and colorless leaves indicate that 

 the absorption values of both of these obey Lambert's law (104o). 

 Seybold has calculated the thickness of the chloroplast layers in order 

 to determine the number of these bodies through which a ray of light 

 may pass successively. He found for Tropaeolum majus 7, Phaseolus 

 multiflorus 5, Ricinus communis 9. A single chloroplast, it was found, 

 absorbs about 30 per cent of the incident light, the second about 21 per 

 cent, the third a further 15, the fourth 10 per cent, beyond that the 

 percentage absorption is very Uttle, so that it may be concluded that 

 the number of chloroplasts in the layer beyond the fourth plays a rela- 

 tively small role in the absorption of light. Transmission values are 

 the same for a parallel beam of light and for diffuse light; there is no 

 evidence that there is a Callier effect produced by the chloroplasts in a 

 leaf (1046). 



