74 BOTANY 



cilia are outgrowths of the membrane, and are not connected with 

 the protoplast. Only in rare instances are the cilia large enough 

 to be detected in the living cell, and recourse must be had to various 

 fixing and staining agents in order to demonstrate their presence. 

 Some of the larger Bacteria show undulatory and creeping move- 

 ments, very similar to those of certain Schizophycese. 



The cells of the Bacteria may be globular e.g. Micrococcus ; but 

 more commonly they are rod-shaped, either straight e.g. Bacillus, 

 or curved e.g. Spirillum (Fig. 51). 



Reproduction 



The reproduction in the Bacteria is mainly by transverse fission, 

 which may be repeated at intervals of half an hour or less, so that 

 they multiply with great rapidity under favorable conditions, a 

 single cell thus being able to give rise to several millions in the 

 course of twenty-four hours. This accounts for their extraordinary 

 multiplication in decomposing organic substances. Fission is accom- 

 plished by the formation of a delicate partition wall across the 

 middle of the cell. The two new cells may separate at once, or they 

 may remain together for a time, forming chains of cells. In case a 

 vacuole is present, this may become divided before the division wall 

 is formed, or the division of the vacuole may be repeated, and a 

 series of division walls are then formed in rapid succession. 



Spores. Many Bacteria produce at the end of their growing period special 

 resting cells or spores (Fig. 51, B), which arise within the cell, appearing first as 

 a minute, glistening speck, which gradually enlarges, absorbing into itself the 

 protoplasmic contents of the cell, which is finally left filled only with a watery 

 fluid in which the spore lies. The latter has a firm membrane enclosing a mass 

 of apparently homogeneous, very dense protoplasm. These spores are extraordi- 

 narily resistant, and sometimes can endure without injury a temperature above 

 the boiling point of water for several hours. On germinating, the outer mem- 

 brane is burst, and the contents escape as a new cell, which at once begins to 

 grow and divide, thus starting a new generation of Bacteria. 



A second form of spores, the so-called arthrospores, have been described, but 

 these seem to differ but little from the ordinary vegetative cells. 



Gonidia. In some of the large filamentous Bacteria, e.g. Cladothrix, the 

 cells, which are enclosed in a tubular sheath, sometimes divide into smaller cells 

 (gonidia) which are discharged from the sheath and grow into new individuals. 



Nothing resembling any form of sexual reproduction is known 

 among the Schizophyta. 



Biology of Bacteria 



No other group of organisms is capable of existing under such dif- 

 ferent conditions as do the Bacteria. One group of the Nitrogen 

 Bacteria forms an exception to the general rule that only green 



