NUTRITION IN THE LOWER PLANTS 85 



moving from the waters of the earth materials found in excess. 

 As a source of food supply to man and the higher animals they are 

 of no importance whatever, but the light they throw upon possible 

 developments of life in places devoid of light or before the existence 

 of green plants upon the surface of the earth is extremely impor- 

 tant. These chemosynthetic forms are the only organisms in- 

 dependent of light and green plants, which thus permits them to 

 occupy a unique place in nature. 



QUESTIONS 



1. What is the method of selective culture? 



2. Distinguish between antisepsis and asepsis. 



3. What is the difficult problem in connection with chemosynthetic bac- 

 teria? 



4. Which cause more animal diseases — bacteria or higher fungi? Which 

 more plant diseases? Why this difference? 



5. What is the relation between the size of bacteria and their high phys- 

 iological activity? 



6. Lichens are greener in damp than in dry weather. Why? 



7. Why are lichens thinner than most fleshy fungi? 



8. As stated above, the blue-green algae are among the simplest autotrophic 

 photosynthetic forms. They are commonly found in hot springs. How can 

 this be explained? 



9. While it was previously thought that a given lichen could be made from 

 a fungus and any one of several algae, Chodat (1930) has shown that this is 

 not the case; the lichen association is very specific. Does this throw any light 

 on the nature of the symbiosis? 



10. What is meant by the statement (p. 84) that the chemosynthetic 

 forms may "be of extreme importance ... in the organic cycles?" 



REFERENCES 



Baas-Becking, L. G. M., and Parker, G. S. — Energy relations in the me- 

 tabolism of autotrophic bacteria. Physiol. Rev., 7:85, 1926. 



Church, A.— The lichen symbiosis. Jour. Bot., 58:213 and 262, 1920. 



Dufrenoy, J. — The endotrophic mycorrhlza of Ericaceae. New Phyt., 16:222, 

 1927. 



Ellis, D. — The structure and life history of the sulphur bacteria. Proc. Roy. 

 Soc. Edinburgh, 44:153, 1924. 



Harder, E. C. — Iron-depositing bacteria and their geologic relations. U. S. 

 Geol. Survey Prof. Paper No. 113, 1919. 



Knudson, L. — Physiological study of the symbiotic germination of orchid 

 seeds. Bot. Gaz., 79:345, 1925. 



Lipman, J. G.— The oxidation of sulphur by microorganisms. Ind. and Eng. 

 Chem., 15:405, 1923. 



McDougal, W. — Symbiosis in a deciduous forest. Bot. Gaz., 73:200, 1922- 



