SYMBIOLOGY THE BIOLOGICAL RELATIONSHIPS OF ORGANISMS 155 



the mutualistic association of alga and fungus. No one has yet succeeded 

 in forming a lichen by associating a true alga (Cystococcus) with a true 

 ascomycetous fungus. If this were possible we might reasonably excepL 

 spontaneously synthetic lichen formations in nature, which is certainly 

 not the case. Lichens invariably arise from preexisting lichens. Some 

 authorities state that a fungus may attack Nostoc colonies and transform 

 them into collematous lichens but this statement requires verification. 



Therefore, it would appear that the most plausible and reasonable 

 attitude to take toward lichen classification is to consider them as a 

 distinct class. This is the conclusion reached after a careful study of the 

 morphology (gross and minute) and ecology of the more important 

 representatives of this very interesting group of plants. 



Future experiments may demonstrate that the living inclusions of 

 the cell constitute a symbiotic association of what were once independent 

 organisms which entered into a mutualistic association which has now 

 become so highly specialized that we fail to recognize their ancestral 

 relationships and origin. As already stated, we have not been able to 

 induce any of these living cell inclusions to continue existence outside 

 of the living cell of which they are a part. Some years ago Reinke ex- 

 pressed the opinion that some skilled scientist of the near future would 

 succeed in cultivating chlorophyll bodies in artificial media. We know 

 that Carel and others have succeeded in inducing tissue proliferation in 

 artificial media. 



IV. Compound Symbiosis 



By compound symbiosis is meant the association of two or more 

 different types or forms of symbioses. Thus we may have two or more 

 organisms mutualistically associated with each other, but forming a com- 

 mon antagonism with the host. It has long been recognized that most 

 of the infections are not simple, but rather multiple. In tuberculosis 

 of the lungs, the bacillus of tuberculosis is not by any means the only 

 infecting organism which is present, other bacteria are present, also 

 yeasts and molds. The leprosy bacillus will not thrive unless associated 

 with certain symbionts, as amebae, body cells, and leprous substance 

 or tissue. The Boas-Oppier bacillus is a fairly constant associate with 

 cancerous tissue and this organism is therefore antagonistic to the cancer, 

 and both are commensal upon the body of the cancerous patient. In 

 Monostomum bijugum, a parasitic worm found in birds, it is known that 

 two individuals always occur together. Most abscesses contain from 

 several to many common infecting organisms. The Staphylococcus 

 group acting as the pioneers, preparing the way for the entrance of the 

 other organisms, which feed upon the products resulting from the primary 

 infection. 



