THE BACTERIA 



279 



cells divide up for reproductive purposes into small 



round bodies (cocci) (see Fig. Ill, B and C), which are 



said to pass through a swarming 



stage. Endospores are not found 



in any of these forms, but in some 



of them it appears that cells of the 



filament may thicken their walls 



and serve as resting-spores (arthro- 



spores) exactly as happens in Nostoc. 



The relations of these organisms to 



the typical Bacteria,as represented by 



^. subtilis, is quite an open question, 



though on the other hand theiraffinity 



to the Cyanophyceae seems clear. 



Before leaving the Bacteria, it 

 may be mentioned that while the 

 great majority are either sapro- 

 phytes or parasites, a few have been 

 found capable of deriving their food 

 entirely from inorganic substances. 

 In some of these cases carbon-dioxide 

 is decomposed under the influence 

 of light, with the help either of true 

 chlorophyll or of a purple pigment 

 which seems to have similar func- 

 tions. Another member of the 

 group is able to obtain its carbon- 

 aceous food from inorganic carbonates 

 without the aid of light, a power possessed by no 

 other organisms at present known. The same Bacteria 

 in which this remarkable property resides are of great 

 importance in another respect, as they bring about the 

 oxidation of nitrogen, thus forming the nitrates in the soil. 



FIG. Ill . Cladothrix 

 dichotoma. A, 



branched vegetative 

 filament. Magnified 

 about 450. B, forma- 

 tion of cocci in a 

 filament. Magnified 

 about 700. ^ C, escape 

 of the cocci. Magni- 

 fied about 700. (After 

 Zopf.) 



