164 PRACTICAL BOTANY 



Sometimes these are present in sufficient numbers to cause the 

 entire cell to have a woolly appearance. In other cases but 

 one or a few of these flagella are present. These are organs 

 of locomotion. 



151. Motility. Many kinds of bacteria can move from place 

 to place by means of the hair-like flagella. The rate of their 

 movement, which varies greatly, may be strikingly rapid. 

 " The typhoid bacillus may travel a distance of 4 mm. (about 

 J inch), or about 2000 times its own length, in one hour ; the 

 cholera spirillum may attain for short distances a speed of 

 18 cm. (about 7 inches) per hour," l a speed that is 45 times 

 as great as that of the typhoid bacillus. There are other 

 spirillum forms that move with great rapidity. These dis- 

 tances may seem short, but if put in terms of the actual length 

 and bulk of the organism, they become more significant. If a 

 man should travel as many times his own length as the typhoid 

 bacillus or as the cholera spirillum (assuming that the cholera 

 spirillum is of length similar to the typhoid bacillus, though 

 it really does attain a much larger size), how far would he 

 travel in one hour? 



152. Reproduction. The usual method of reproduction is by 

 fission, in which the bacterial cell divides into two new cells, 

 each of which is a new individual. The newly formed cells 

 usually separate soon after being formed. Sometimes, how- 

 ever, they continue to divide for a number of generations 

 without becoming separated, thus producing a chain or fila- 

 ment of plants. In a very short time the new plants become 

 full-grown and ready again to divide. In the case of some 

 kinds of bacteria newly formed individuals divide within 

 twenty minutes to a half hour after they themselves are 

 produced. Thus two or three generations may be formed 

 within an hour's time. The possibilities of this rate of repro- 

 duction are enormous. If all conditions were to remain en- 

 tirely favorable for reproduction, a bacterium which divides 

 but once an hour would in two days produce offspring 



1 Jordan, E. O., General Bacteriology, 1908, pp. 59-60. 



