CHAPTER VI 



MiCROSYMBIOSIS 



Long before it was discovered that bacteria enter into 

 symbiotic relations with plants and animals, it was known 

 that single-celled plants, particularly the algae, may be 

 symbiotic guests in the tissues of certain animals. Due to 

 their larger size and more distinctive characteristics, the 

 algae are more readily detected in symbiosis than bacteria, 

 and consequently they are better known in microsymbiosis. 

 The morphologic and physiologic responses that are indi- 

 cated in these symbioses vary within wide limits. The 

 ''degree" of symbiosis also varies. This variation extends 

 all the way from an occasional presence of the symbiont to 

 absolute symbioses. The study of microsymbiosis has 

 been pursued by a number of investigators during the past 

 twenty-five years. More recently Paul Buchner (1921) 

 has rendered an invaluable service to investigators by his 

 comprehensive and analytical review of the Uterature. A 

 considerable portion of the data which will be catalogued 

 in this chapter has been taken from Buchner's treatise. 

 The reader who desires more detailed descriptions than 

 will be found here is referred to this comprehensive mono- 

 graph (in German). 



The study of microsymbiosis, perhaps, had its beginning 

 in the interest aroused in the nature of the chlorophyl that 

 occurs in a number of lowly animals. Quite a few of these 

 animals are familiar to the general biologist on account of 

 their green coloration {amoeba viridis, fresh water sponges, 

 hydra viridis, and other coelenterates and marine worms). 

 For a long time the green color was not associated with 

 chlorophyl. Later, discussion arose as to its nature and 



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