16 RELATIONSHIPS OF THE COCCACE^ 



which constitute species among the higher forms. Yet 

 even in reference to complex plants and animals the con- 

 ception of purely environmental types is gaining ground. 

 It is not in connection with bacteria that Jordan and 

 Kellogg (1907) speak of " Ontogenetic species held for 

 a number of generations true to a type simply because 

 the environment, the extrinsic factors in the development 

 of all the individuals in these successive generations, are 

 the same." Ortmann (1908) has recently proposed a 

 difference of habitat as a definite criterion of species 

 among the higher plants. Speaking of types of orchids 

 he says, " If further studies should show that there is 

 segregation, geographical or ecological, between these 

 forms, then they are species; if not, they are varieties, 

 which fact then also will be expressed in their morpho- 

 logical condition, one form running into the other at 

 least in certain parts of their ranges." 



Among the bacteria ontogenetic species are common. 

 Every bacteriologist recognizes types of structure and 

 function definitely associated with special habitats; 

 pathogenic and agglutinative powers for example offer 

 striking instances of direct adaptation. Evidence accu- 

 mulates too that a change of environment leads to a 

 loss or gain of biochemical power. Peckham (1897) 

 found that the action of colon bacilli upon pepton is 

 highly variable. Horrocks (1903) observed that B. coli, 

 kept in water for several months, showed only a feeble 

 indol reaction and a delayed action on milk and neutral 



