282 PARf III. THE CLASSIFICATION OF PLANTS. 



Although a special name has been given to each of the multi- 

 farious forms assumed by the Schizomycetes, it must not be 

 assumed that each form to which a name has been given con- 

 stitutes a distinct species. On the contrary, the Schizomycetes 

 are highly polymorphic, and the various simpler forms are, for 

 the most part, merely phases in the life-history of the more com- 

 plex forms. The Schizomycetes may be classified, in accordance 

 with these facts, as follows : 



1. Coccacece : exist in the free coccus-form, or in the zoogloea-stage. 



Leuconostoc is the only form which has been fully investigated. 



2. Bacteriacece : exist in the coccus-form, the bacterium-form and the 



bacillus-form ; any of which may pass through a zoogloaa-stage. 



Genera: Bacterium (e.y. Bacterium Termo) ; Clostridium (e.g. Clostri- 

 dium butyricum, causing butyric fermentation) ; Bacillus (e.g. Bacillus 

 subtilis) developed in infusions of hay. 



3. Leptothrichiece ; unbranched, attached, filamentous forms ; giving rise to 



coccus, bacterium, and spiral forms, which may pass through a zoogloea- 

 stage. Genera : Leptothrix, Beggiatoa, Crenothrix. 



4. Cladothrichiete : resemble the preceding, but the attached filaments are 



(spuriously) branched. Genus, Cladothrix. 



The Schizomycetes multiply mainly by cell-division (whence their 

 name), and they do so with great rapidity under favourable con- 

 ditions ; the nucleus undergoes mitotic division in connexion with 

 this process. In many forms reproduction is also effected by means 

 of spores (e.g. Leuconostoc mesenterioides, Bacillus subtilis and 

 Anthracis, Clostridium butyricum). Each spore is formed from a 

 cell, the protoplasmic contents contracting from the cell-wall and 

 surrounding themselves with a thick proper wall ; the spore is set 

 free by the decay of the old cell-wall. Spore-formation generally 

 takes place in the zoogloea-stage, and is promoted by conditions 

 which are unfavourable to growth and multiplication by division. 

 The vitality of the spores is remarkable, being retained under con- 

 ditions, such as extremes of temperature, desiccation, etc., which 

 would prove fatal to the organisms themselves. 



The most conspicuous feature in the physiology of the Schizomy- 

 cetes is their capacity for decomposing organic compounds, indu- 

 cing various fermentative processes, such as the lactic and the 

 butyric fermentation of various kinds of sugars, etc., (but never 

 the alcoholic fermentation), and the putrefactive fermentation of 

 complex nitrogenous organic substances, such as proteids, etc. Some 

 are parasitic in the bodies of animals, such as tiarcina Ventriculi, 

 Leptothrix buccalis which causes decay of the teeth, and the various 



