162 



PRACTICAL BOTANY 



great variations in length and diameter, and spiral forms hav- 

 ing from a fraction of one spiral to many spirals. Further- 

 more, spherical forms may become piled upon one another 

 so that colonies result, and rods may be joined (Sect. 152) in 



FIG. 150. A group of bacteria 



A, Bacillus typhosus, from a six-hour-old culture upon nutrient agar. In such 

 cultures the main body of the bacillus is short and the cilia are relatively prom- 

 inent; magnified 1000 diameters. B, Micrococcus tetragenus, three groups each 

 of four individuals, each showing the characteristic arrangement; the larger 

 bodies are portions of the pus in which the bacteria occur. C, Bacillus tubercu- 

 losis; the very slender bacilli are shown among particles of sputum. D, Proteus 

 vulgaris, a widely distributed saprophytic bacillus. E, Pneumococcus, some 

 individuals of which have been inclosed and partially digested by the large 

 white blood corpuscles (phagocytes). F, Staphylococcus aureus, a small spheri- 

 cal bacterium usually arranged in chains; magnified 1000 diameters. Modified 

 from Jordan's " General Bacteriology " 



such a way as to construct filaments. Within these groups 

 many species of bacteria are known. One high authority, 

 Migula, considers that there are 1272 distinct species of bac- 

 teria, most of which belong to the bacillus type. 



