PHYLOGENETIC ADAPTATION OF THE PIGMENT SYSTEM 421 



carotenoids) . Fucoxanthol absorbs at least some green light, while the 

 red phycoerythrin is eminently suitable for the absorption of the spectral 

 region transmitted by thick layers of sea water. 



In order to absorb efficiently the light transmitted by the surrounding 

 medium, a pigment must have a color complementary to that of the 

 medium. Therefore, Engelmann called this phenomenon cornplementary 

 chromatic adaptation, to distinguish it from mimicry, a chromatic adapta- 

 tion in which organisms acquire a color which blends with the surround- 

 ings. Oltmanns (1893, 1905) opposed Engelmann's theory and suggested 

 that the vertical distribution of algae is determined by the intensity, 

 rather than by the color of the prevailing light. This controversy has 

 continued for 50 years, and extended from the initial problem of algal 

 distribution to two related problems: (a) the participation of phycobilins 

 as sensitizers in photosynthesis (without which the chromatic adaptation 

 of algae would have no raison d'etre); and (6) the "re-adaptation" of 

 colored algae in artificial light. In this discussion, Gaidukov (1903, 

 1904, 1906), Boresch (1919), Harder (1917, 1922, 1923), Ehrke (1932), 

 Seybold (1934), and Montfort (1934, 1936) have supported Engelmann's 

 hypothesis, whereas von Richter (1912) and Sargent (1934), among 

 others, have supported the concept of Oltmanns and denied the reality 

 of chromatic adaptation (and incidentally also the capacity of the 

 phycobilins to serve as sensitizers in photosynthesis). 



The discussion of ontogenetic re-adaptation is postponed to the next 

 section of this chapter (page 424), and that of the active participation 

 of phycobilins in photosynthesis — to which a positive answer seems 

 certain — to volume II, chapter 30. As to the original problem, Harder 

 (1923) was probably right in his suggestion that both intensity and color 

 of light play a part in the adaptation of algae to deep waters. According 

 to volume II, chapter 22, the light field in a depth of 20 meters is not 

 only free from red and violet radiations, but is also reduced in total 

 intensity by a factor of 20 or more. No wonder that deep sea algae are 

 typical "shade plants," with a high content of pigments, and are sus- 

 ceptible to injury when exposed to direct sunlight. However, the 

 composition of the pigment system of these algae corresponds not only 

 to the low general light intensity, but also to the relative weakness of 

 red and violet rays. The situation is complicated by an interplay of 

 heredity (which tends to impose on the organism a rigid composition of 

 the pigment system) and of the capacity for individual variations, which 

 tends to adjust the pigments of a species or individual to the concrete 

 conditions under which it finds itself. Brown or red algae found on the 

 surface often are almost pure green. According to Lubimenko (1926, 

 1928), the comparison of red algae of one and the same species found at 

 different levels shows a systematic increase in the concentration of all 



