THE NATURE OF BACTERIA. 



2 9 



FIG. 7. 



confusion. Many hundreds of species have been described by 

 different bacteriologists, but there is great difficulty in giving 

 any distinctive description of such minute organisms, which 

 have so few characters, and it is quite 

 uncertain whether these many hundreds 

 of described species represent entirely dis- 

 tinct forms or whether they should be 

 reduced to a much smaller number of 

 species. It is frequently uncertain whether 

 a species described by one bacteriologist 

 is the same as that described by another 

 under the same name. The difficulties 

 which have been found in the way of a 

 proper description and classification of 

 the species of bacteria have been hitherto 

 insurmountable, and at the present time 

 the subject is in such extreme confusion 

 that no one except an expert can under- 

 stand it. Fortunately for our purpose in 

 studying agricultural bacteriology this 

 confusion of species is of no importance. 

 Agricultural bacteriology is at present 

 concerned in the results of the action of microorganisms, and 

 is only slightly concerned with the problem of the specific 

 characters of bacteria. All that is necessary for us to know 

 in connection with our subject will be referred to in the sepa- 

 rate sections in the following pages, and the subject of the 

 classification of bacteria may be left without further consid- 

 eration. 



As indicated by this classification, bacteria, although in earlier 

 years frequently called animals, are to-day universally regarded 

 as plants. The reason for calling them plants is not at first sight 

 evident. They are colorless, unlike most plants. They are 

 frequently endowed with a power of independent motion, a 



Actinomyces : a, a small 

 colony ; b, single rods. ( Bos- 

 trom. ) 



