CLASSIFICATION OF BACTERIA 37 



genera; and a genus is composed of species. By this system each 

 variety of plant has a specific place within the classification. We 

 have seen that the plant kingdom is commonly divided into four 

 divisions, one of which is the Thallophytes. This division is made 

 up of classes; the classes, of orders. The orders, which comprise 

 one of these classes, are made up of that great variety of plants 

 which we know as bacteria. Before we consider further these 

 orders it is best to consider the methods used in naming bacteria 

 and the factors used in classifying them. 



Nomenclature. — Early in the history of botany the worker 

 used a descriptive phrase in referring to a species of plants. A 

 different worker would use a different word or phrase to describe 

 the same plant. This method resulted in confusion, for it was 

 often impossible to determine whether both writers were referring 

 to the same plant or to different plants. To overcome this diffi- 

 culty the great Swedish naturalist, Linnaeus, devised the binomial 

 system of naming plants, so-called because each species is given 

 two names. The first is the name of the genus and the second 

 the name of the species. The first is common to many; the sec- 

 ond name is specific. However, it will be noted in botanical 

 nomenclature the specific name comes last, or in other words, it 

 is the reverse of what it is in family names. First, is given the 

 name of the genus which must be capitalized and which may be 

 written in full or abbreviated. This is followed by the individual 

 or name of the species. This is written in full and with a small 

 letter. Usage at times has sanctioned the use of a capital where 

 the name is a proper noun. However, even here it is better to use 

 a small letter. In order to avoid confusion and to make more 

 clear what specific plant is referred to there is often placed after 

 the name of the species the name, or an abbreviation of the 

 name of the botonist who first used the name for the species. 

 Following this system the name for wheat would be written 

 Triticum. sativum^ or T. sativum.. That for the potato is written 

 Solanufn tuberosum, or S. tuberosum,. Unfortunately, this system 

 is much less satisfactory when applied to microorganisms. 



Difficulties with Bacteria — ^The difficulties inherent in the 



