EMPIRICAL PLANT SPECTRA 



691 



spectra" or "absorption spectra," respectively; or one may use colorless 

 specimens as "blanks," determine To and i^o (or So = To + ^o), plot T/To, 

 R/Ro or .Sy,So against X and designate these curves as "transmission," 

 "reflection" or "absorption" spectra, respectively — but, although each of 

 these plots is legitimate as representation of a certain property of the 

 specimen investigated, they are all different. (For example, fig. 22.11, p. 

 686, shows the transmission spectrum and the reflection spectrum of the 

 same leaf.) The true absorption spectrum on the other hand is an intrinsic 

 property of a molecular species (or, in the case of a mixture, the average of 

 intrinsic properties of several molecular species). 



We will discuss the quantitative analysis of the empirical "leaf spectra" 



1.4 



L2 

 1.0 



§0.6 



_i 



0.4 

 0.2 



0.7 

 0.6 

 0.5 

 04 

 0.3 

 0.2 

 0.1 



400 440 480 520 560 600 640 680 720 

 WAVE LENGTH, m/i 



400 440 480 520 560 600 640 680 720 

 WAVE LENGTH, m/i 



Fig. 22.22. Tran.sniission .spectrum of Fig. 22.23. Transmission spectrum 



{To/T) Chhrella suspension (after Emer- {To/T) of suspension of Chroococcus 

 son and Lewis 1943). (blue alga) (Emerson and Lewis 1943). 



or "cell spectra" below, in section 4. First, we will present a selection of 

 experimental results, and discuss their qualitative aspects. 



Spectral data on leaves of land plants have been collected by Ivanovski 

 (1907, 1913), Willstatter and Stoll (1918), Ursprung (1918), Wurmser 

 (1921), Lubimenko (1927), Seybold and co-workers (19321-2, 1933, 1934, 

 1936, 1942i'2, 1943), Meyer (1939), Loomis et al. (1941, 1949), Iljina (1946) 

 and French et al. (1946), among others. The curves on pages 686 to 689 

 are from some of the more recent investigations. Figure 22.17 shows 

 the transmission spectrum of the water-filled leaves of the aquatic plants 

 Elodea and Potomageton, according to Seybold (1933). Transmission 

 spectra of algal thalli were measured by Reinke (1886), Engelmann (1884, 

 1887), Gaidukov (1904), Wurmser (1926) and Seybold and co-work- 

 ers (1934, 19421--, 1943). Figures 22.18-22.20 show curves given by 



