190 Minnesota Plant Diseases. 



magnifications in order to observe and study them. The bac- 

 terial plants may differ somewhat in form and to these various 

 forms names have been applied, and upon them the classi- 

 fication of the bacteria was formerly based. It is now rec- 

 ognized, however, that several forms may appear in the same 

 life-story under differences of conditions, thus rendering the 

 former classification unsatisfactory. An approximately spheri- 

 cal bacterium is known as a coccus, a short, rod-like form is 

 known as a bacterium, in the narrower sense, and the long rod 

 form is a bacillus. Some forms are, moreover, comma-shaped ; 

 others are undulate or wavy in appearance, while still others ap- 

 pear much like corkscrew or long-drawn spiral coils. These 

 plants may differ, moreover, in the manner in which colonies 

 are formed. All bacteria in the broader sense multiply chiefly 

 by simple division of the cell into two, the resulting parts split- 

 ting away from each other hence the name fission plants. By 

 such divisions filaments of cells may be built up, or by division 

 in two planes, plates of cells, or when division in three planes 

 takes place masses of cells are produced. As the external walls 

 of bacteria are frequently gelatinous, sheaths are formed which 

 serve to bind the plants together in such filaments, plates or 

 masses. A larger gelatinous colony may thus be built up and 

 is then known as a zoogloea. One sees among the bacteria a 

 great variety of habits ; a large number inhabit fluid media. 

 As a special means for dissemination many of such forms have 

 lash-like projections of the protoplasm which whip around in 

 the water and propel the plant cell about. 



Multiplication and reproduction. The fission method of 

 multiplication which is common in the bacteria is a very effi- 

 cient one. It is also common to certain groups of blue-green 

 algae. In bacteria the successive splittings into cells may fol- 

 low with some rapidity, e. g., under the most favorable condi- 

 tions the hay bacillus completes a division in twenty minutes. 

 It has been calculated that if a bacillus two-thousandths of a 

 millimeter in length were to divide uninterruptedly at the rate 

 of once every thirty minutes, at the end of five days the volume 

 of the resulting bacteria would fill all of the ocean beds of the 

 globe. Competition and unfavorable conditions, of course, 

 prevent such disastrous results, but the possible rapidity of 



