26 



BACTERIA AND SOIL FERTILITY 



layer of cells. These are the micrococci. Others may divide in 

 one plane followed by a second division which is not always at 

 right angles so that the organisms form an aggregate which has 

 the appearance of a bunch of grapes. These are the staphylococci. 

 Still other organisms may divide in three planes, thus giving rise 

 to packets of cells, a condition similar to that which one would 

 have if four marbles were placed on a level surface and four 



■^I'^iiiiHfi, 



Fig. 8. — Sarcina (after Gruber). 



Fig. 9. — Large Spirilla (after Novy). 



Others placed upon them. These are the sarcina, and they have 

 the appearance of a bale of cotton. 



A bacterial generation is taken as the time required for a ma- 

 ture cell to divide and the resulting daughter cells to reach ma- 

 turity. This process may be completed in half an hour — at times, 

 even more rapidly. Under less favorable circumstances it may be 

 much longer. It has been estimated that if bacterial multiplica- 

 tion went unchecked the descendants of one cell would in two 

 days number 281,500,000,000, and that in three days the descen- 

 dants of this single cell would weigh 148,356,000 pounds! It 

 has been further estimated by an eminent biologist that if proper 

 conditions could be maintained for their life activity, in less than 

 iive days they would make a mass which would completely fill 

 as much space as is occupied by all of the oceans on the earth's 

 surface, if the water has an average depth of one mile! 



