THE STORY OF THE BACTERIA. 31 



place. Usually at the end of this time, if all 

 goes well, there will be a growth of the bac- 

 teria on the potato so large as to be quite 

 visible to the naked eye. This growth, or 

 "colony," as it is called, which is made up of 

 myriads of individual bacteria, the offspring 

 of those planted, in many cases presents very 

 characteristic ways of growing or special 

 colors, etc., characters often by which particu- 

 lar species of bacteria may be distinguished 

 from all others, even without the aid of the 

 microscope. This gross appearance of the 

 growing colonies is useful in the recognition 

 of species which under the microscope look 

 very much alike. Just as in agriculture, if 

 one were in doubt as to two specimens of seed 

 which closely resembled one another say tur- 

 nip and rape, for example by sowing them in 

 the ground and observing the resulting plants, 

 all doubt would be removed. 



In thus planting the invisible and minute 

 bacteria, and allowing them to grow until such 

 large masses of colonies are formed that we 

 can readily see and study them with the naked 

 eye, we are realizing in another field a project 



