NUTRITION 



369 



sunlight, i.e. a narrow bar of light dispersed into a band of different 

 wave lengths, each group of waves produces its appropriate effect and 

 we see a band of blending colors, dark red at one end, running through 

 red, orange, yellow, green, blue, indigo, violet, and ending in the dark- 

 est violet. On interposing a leaf in the path of the light, there appear 

 across the spectrum dark strips due to the partial or complete stoppage 

 of the energy. Similar absorption bands, slightly displaced, are seen by 

 using in the same way an alcoholic solution of chlorophyll (fig. 648). 



a B C D E b F G h 



Fig. 648. — Absorption spectra: A, chlorophyll of Allium ursinum in alcohol; B, 

 chlorophyll of English ivy (Hedcra Helix) in alcohol; C, chlorophyll of Oscillatoria in 

 alcohol; D, carotin, i, 2, 3, 4, absorption bands of chlorophyllin; /, II, 77/, absorp- 

 tion bands of carotin; EA, end absorption. The lettered broken lines mark the position 

 of the principal absorption lines of the solar spectrum (Fraunhofer linos); the numbered 

 solid lines form a scale from which wave lengths (X) in millionths of a millimeter may be 

 found by adding a cipher; note the increasing dispersion from left (red) to right (violet). 

 — After Kohl. 



These absorption bands are as follows: 1, in the red a wide black one, its wave 

 lengths (X) being 670-635 MM 1 ; 2, a narrower and less intense one in the orange, 

 X = 622-597 mm; 3, in the yellow, a band much lighter than 2, and shading 

 out on the sides, ^ = 587-565 fifi; 4, a faint band in the green, not always 

 to be seen, and probably due to decomposition products, X = 544-530 nf- Or- 

 dinarily the other three blend into one, and there are no visible waves left beyond 

 the blue (X = 495-420). By very careful manipulation, using dilute solutions in- 

 stead of a leaf, they can be distinguished, their limits not being sharply marked. 

 1 The exact location of the bands varies. 1 /x/j. = o.oooooi mm. 



C. B. & C. BOTANY — 24 



