32 The Story of the Bacteria 



material is spread upon the cut surface of the 

 potato, and the latter is covered again and set 

 away for a day or two in a warm place. Usu- 

 ally at the end of this time, if all goes well, 

 there will be a growth of the bacteria 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 character- 

 istic ways of growing or special colors, etc., 

 characters often by which particular 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 turnip 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 



