96 SYMBIONTICISM AND THE ORIGIN OF SPECIES 



each other, and again join in the production of a daughter 

 Uchen. In the next higher group, reproduction of the two 

 symbionts is still independent, but an accessory method 

 of multipHcation is represented by a process of budding. 

 The daughter lichens produced by this method contain 

 both of the symbionts from the first. In the higher groups 

 of lichens, a reproductive organ, the "soridium" is formed. 

 Both symbionts supply materials in the formation of the 

 reproductive elements. In these higher Hchens the sym- 

 biosis has become absolute, and reproduction is no longer 

 independent. The relationships in these three groups of 

 lichens appear to indicate that there is a gradual develop- 

 ment towards a complete interdependence of the two sym- 

 bionts. 



In the more lowly lichens, there is a possibihty of inde- 

 pendent existence of the two symbionts. In the higher 

 lichens, the two symbionts are incapable of independent 

 existence in nature. There is no question regarding sym- 

 biosis in the lichens, as the symbionts are readily distin- 

 guishable. Here is an example of an entire group of or- 

 ganisms whose origin unquestionably depended upon the 

 establishment of a symbiotic relationship. 



The symbiotic relationships in which luminiferous bac- 

 teria are the definitive symbionts, have produced morpho- 

 logic responses in the host that are of the greatest signifi- 

 cance in the theory of Symbionticism. In a number of 

 these symbioses, definite organs have been formed in the 

 host, associated with luminescence and harboring the lumi- 

 niferous symbionts. These organs vary in complexity 

 in different animals. In some of the beetles, the organ 

 consists of two kinds of cells — the bacteriocytes, containing 

 the luminferous symbionts, and the "urate cells" which 

 become associated with them and have a subsidiary func- 

 tion in connection with the organ as a whole (reflector). 

 The cells that harbor the luminiferous symbionts are modi- 



