ALLIED AND MISCELLANEOUS PRODUCTS 193 



pounds of pigments with proteins (presumably albumins). Phyco- 

 cyanin is found chiefly in the blue-green alga?, while phycoerythrin 

 is characteristic of the red. There are evidently two or three 

 separate phycocyanins with separate shades of color and distinct 

 absorption spectra. Phycocyanins have been reported also in some 

 red algae, while phycoerythrin has been reported in some of the 

 blue-greens; but Danilov thinks these are related pigments and 

 not genuine phycocyanin and phycoerythrin. Both these pigments 

 are strongly fluorescent. The brown algae have been said to con- 

 tain a similar pigment, phycophsein, but some biochemists (Hooker 

 and others) have doubted its existence and believe the color of 

 these algae is due entirely to the carotinoid pigment, fucoxanthin. 



Physiological Significance of the Pigments.— Since pigments 

 vary so much in different plants, they might be expected to have 

 a variety of functions, if any. In considering the physiological 

 importance of a material, it is often difficult to decide whether it 

 really has a function or whether it may simply be the result of 

 environmental (external or internal) changes and have no func- 

 tion, i. e., it is difficult to decide whether it has survival value 

 or is merely neutral in its effect. What is it for? is the great 

 question. 



The pigments have been credited with these uses: 



1. They aid in respiration. In the blood during animal respira- 

 tion the hemoglobin is changed to oxyhemoglobin on the addition 

 of oxygen in the lungs, with the reverse change in the tissues. The 

 red pigment thus serves as an oxygen carrier, and Palladin (1909) 

 has sought such a function in the plant pigments. The relation 

 of carotin to xanthophyll, and the changes from red to blue antho- 

 cyans under the action of oxidizing and reducing enzymes, make 

 such a function seem plausible. The relation of lycopersicin to 

 the temperature has already been mentioned (Chap. V), and the 

 same failure to become red occurs in the absence of oxygen. The 

 connection between the anthocyans and the presence of sugars, 

 which are easily oxidizable substances, also points to a relation 

 between these materials and oxidizing phenomena (Chap. XXV). 



2. They aid in photosynthesis by absorbing light, which may 

 be used in the manufacture of food. Anthocyans absorb some of 

 the rays which the chlorophyll does not and so are complementary 

 to the chlorophyll. The relation of the algal pigments to photo- 

 synthesis has already been discussed (Chap. VI). Here the question 



