BACTERIA AS PLANTS. 33 



ous anomaly. Whereas their closest allies are 

 known only to botanists, and are of no interest 

 outside of their systematic relations, the bacteria 

 are familiar to every one, and are demanding the 

 life attention of hundreds of investigators. It is 

 their absence of chlorophyll and their consequent 

 dependence upon complex foods which has pro- 

 duced this anomaly. 



CLASSIFICATION OF BACTERIA. 



While it has generally been recognised that 

 bacteria are plants, any further classification has 

 proved a matter of great difficulty, and bacteriolo- 

 gists find it extremely difficult to devise means of 

 distinguishing species. Their extreme simplicity 

 makes it no easy matter to find points by which 

 any species can be recognised. But in spite of 

 their similarity, there is no doubt that many 

 different species exist. Bacteria which appear to 

 be almost identical, under the microscope prove 

 to have entirely different properties, and must 

 therefore be regarded as distinct species. But 

 how to distinguish them has been a puzzle. 

 Microscopists have come to look upon the differ- 

 ences in shape, multiplication, and formation of 

 spores as furnishing data sufficient to enable 

 them to divide the bacteria into genera. The 

 genus Bacillus, for instance, is the name given to 

 all rod-shaped bacteria which form endogenous 

 spores, etc. But to distinguish smaller subdi- 

 visions it has been found necessary to fall back 

 upon other characters, such as the shape of the 

 colony produced in solid gelatine, the power to 

 produce disease, or to oxidize nitrites, etc. Thus 

 at present the different species are distinguished 



