296 



ASSIMILATION. 



The instructive similarity between the spectrum of the yellow 

 coloring-matter of chlorophyll and that of the so-called etiolin, 

 or yellow coloring-matter which can be extracted from blanched 

 leaves, is shown in the two figures here given. 



BOP B 1 



T .4011 \wi> SCO I 



iilililiilm illllllniilmiliiii'hl 



^om 



B C 



ill 



D 



ll'lllllMl'lllll 



[illliiiilii iiliiii'iiiii|iiiim 



300 \liM SO' 



iulll 



789. An alcoholic solution of chlorophyll undergoes very little 

 if any change when kept in the dark ; but even a short exposure 

 to strong light destroys its green color, and leaves the liquid 

 pale brown, or nearly colorless. When, however, strong sun- 

 light passes through a solution of chlorophyll before it reaches a 

 second receptacle filled with the same liquid, the first solution 

 protects the second for a considerable time ; and only after the 

 first has lost a portion of its green color can the second be also 

 acted upon. 



790. Sachs ^ has pointed out the interesting fact that green 

 leaves, especially those of delicate texture, become paler when 

 exposed to a very bright light, and resume their deep green 

 color when again subjected to a less intense light. If one leaf 

 is partially' shaded by another, the shaded leaf preserves its nor- 

 mal deep green color, while the leaf exposed to the light grows 

 distinctly paler. This effect, due probably to a change of posi- 

 tion of the chlorophyll grains, can be shown experimentally 

 in the following manner : Fasten closelj- to a green leaf, still 



^ Ber. iiber die Verhandlungen (Math. Phys. Classe) der Siichsischen Ge- 

 sellsch. xi., 1859, 226 ; and also in Experimcntal-physiologie, 1865. 



Fig. 151. The upper spectrum is that of the yellow constituent of chlorophyll ftom 

 Deutzia scabra; the lower, that of the coloring-matter of etiolated barley, in dilute 

 solution. (Kraiis) 



