190 LIVING PLANTS 



atively recent period in the history of plants. 

 Form and odor are much more efficient agents 

 than color in the attraction of animals. 



Chlorophyll converts light into energy by 

 the aid of which the protoplasm which con- 

 tains it is able to build up complex foods. 



The lipochromes are found in leaves and 

 other organs, associated with chlorophyll un- 

 der the name of xanthophyll, in citrus fruits, 

 in some underground members and in fungi 

 and bacteria. The yellow tints of autumn 

 leaves are due to lipochromes. These sub- 

 stances may occur in solid crystalloids in the 

 cell or diffused throughout the protoplasm or 

 suspended in oily drops. The lipochromes 

 probably serve as reserve substances in some 

 plants and in others as a screen against in- 

 tense illumination. Bacteria furnished with 

 a lipochrome pigment are able to occlude com- 

 paratively large quantities of oxygen which 

 may be given off under partial pressure. Cer- 

 tain green and red bacteria are able to carry 

 on food formation by means of a pigment re- 

 sembling chlorophyll in physical and chemi- 

 cal properties. A second pigment which has 

 some of the characteristics of the red color of 

 the algae is also present in these forms. The 

 pigments of the bacteria have been the subject 

 of but little investigation. 



