COLOR 177 



and Sarcina rosea offer examples, liave the 

 power of occluding oxygen from the air, which 

 maybe given off under partial pressure. The 

 pigment is the oxygen carrier and may act in 

 a similar manner after it has been extracted 

 from the organism. The green and purple 

 bacteria of w^hich Bacterium viride and B.pho- 

 tometricum are examples, contain two pig- 

 ments one of which resembles chlorophyll and 

 the other the red coloring matter of the algae. 



The anthocyans comprise a series of sub- 

 stances soluble in water varying from red to 

 blue and violet according to the acid or alka- 

 line nature of the cell sap in which they are 

 always found in solution. Thus a portion of Anthocyans 

 a plant of a blue color from the presence of 

 anthocyan may be changed to a red by im- 

 mersion in an acid solution and the operation 

 ma}' be reversed . Similar changes are often 

 brought about in the petals of flowers by 

 chemical processes set up within the cell. Ex- 

 amples of changes of this character are shown 

 by Pulmonaria, Mertensia, S^^mphytum and 

 willows. 



The anthocyans occur in stems, petioles, 

 flowers, leaves, unfolding shoots, organs ex- 

 posed to low temperatures, and in injured 

 regions. It is quite generalh^ accepted that 

 the pigments embraced in this group are de- 



