BACTERIA AS PLANTS. 25 



bacteriologist calls a colony. But their method of 

 clustering, due to different methods of growth, is 

 by no means always alike, and these colonies 

 show great differences in general appearance. 

 The differences appear to be constant, however, 

 for the same species of bacteria, and hence the 

 shape and appearance of the colony enable bac- 

 teriologists to discern different species (Fig. n). 

 All these points of difference are of practical use 

 to the bacteriologist in distinguishing species. 



SPORE FORMATION. 



In addition to their power of reproduction by 

 simple division, many species of bacteria have a 

 second method by means of spores. Spores are 

 special rounded or oval bits of bacteria protoplasm 

 capable of resisting adverse conditions which 

 would destroy the ordinary bacteria. They arise 

 among bacteria in two different methods. 



Endogenous spores. These spores arise inside 

 of the rods or the spiral forms (Fig. 12). They 

 first appear as slight granular masses, or as dark 

 points which become gradually distinct from the 

 rest of the rod. Eventually there is thus formed 

 inside the rod a clear, highly refractive, spherical 

 or oval spore, which may even be of a greater 

 diameter than the rod producing it, thus causing 

 it to swell out and become spindle formed (Fig. 

 12 c]. These spores may form in the middle or at 

 the ends of the rods (Fig. 12). They may use up 

 all the protoplasm of the rod in their formation, 

 or they may use only a small part of it, the rod 

 which forms them continuing its activities in spite 

 of the formation of the spores within it. They are 

 always clear and highly refractive from contain- 



