372 



BOTANY 



PART II 



disintegrated when the spore is ripe. Spores are not found in all 

 species. 



Order 1. Haplobaeteria. UNICELLULAR BACTERIA 



This includes the great majority of the species. 



Although the cycle of forms passed through in the life-history of a Bacterium 

 is a very simple one, the individual species, which can often be barely dis- 

 tinguished by morphological characters, show great variety in their metabolic 

 processes and in their mode of life. The majority of Bacteria require oxygen for 

 their respiration, and are therefore aerobic ; many can, however, develop without 



this gas, while some species, e.g. 

 the butyric acid bacterium and the 

 tetanus bacillus, are strictly anae- 

 robic and only succeed in the absence 

 of oxygen. Some bacteria produce 

 by their respiration considerable 

 heat ; this is the explanation of 

 the spontaneous heating of damp 

 hay, dung, tobacco, and cotton-wool. 

 In such substrata Bacillus calfactor 

 develops ; it is adapted to live at 

 high temperatures (above 40) and 

 is still motile at over 70 C. (cf. p. 

 277). 



Saprophy tic and parasitic species 

 are distinguished, although a sharp 

 separation is often impossible. In 

 cultures the parasitic forms can be 

 made to lead a saprophytic life on 

 suitable substrata. 



Bacillus suUilis, the Hay bacillus 

 FIG. 295. Bacillus subtilis. a, d, Motile cells and (Fig. 295), which appears as a rule 

 chain of cells ; Z>, non-motile cells and chains of j n the decoction obtained by boiling 

 cells ; c, spores from the zoogloea e (a-dx 1500 ; h . t m ff rf example 

 e x 250. From A. FISCHER, Varies, uber Bac- * ' 



terien ) * e "fe-liistory of a bacterium. 



The spores of this species, which 



withstand the effect of the boiling water, produce on germination rod-shaped 

 swarming cells with cilia on all sides ; these divide and may remain connected 

 in short chains. At the surface of the fluid these swarming cells change into non- 

 motile cells without cilia ; these divide up, giving rise to long intertwined chains 

 of cells. These are associated together in the pellicle covering the surface 

 (zoogloea stage). Spore formation occurs when the nutritive substances in the 

 fluid are exhausted. 



The zymogenous 'or fermentation Bacteria and the saprogenous or decomposi- 

 tion Bacteria are other saprophytic forms. The former oxidise or ferment carbo- 

 hydrates. The latter decompose nitrogenous animal or vegetable substances 

 (albumen, meat, etc.) with the liberation of ill-smelling gases. 



The acetic acid bacteria (Fig. 296 a, b, c) oxidise alcohol to acetic acid. The 

 transformation of sugar into lactic acid is brought about by the rod-like cells of 

 Bacillus acidi lactici (Fig. 296 d). Clostridium butyricum (Fig. 296 e} forms 

 butyric acid from various carbohydrates in the absence of oxygen, while certain 



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