THE RELATIONSHIP OF BACTERIA 117 



sideration, show more points of resemblance to the plants 

 than to the animals. They have been found to resemble 

 certain of the lower plants very closely. The bacteria are 

 now defined to be microscopic, unicellular, non-nucleated plants, 

 devoid of chlorophyll and reproducing by direct fission. In some 

 orders the formation of special reproductive cells known as 

 gonidia occur. Some authors have stated that reproduction 

 also takes place by the formation of endospores. This propo- 

 sition has been discussed in another chapter. 



Bacteria are the most widely distributed and most numer- 

 ous of all living organisms. The surface of the earth and the 

 soil to an average of four feet contain bacteria. The waters 

 on the surface of the earth contain innumerable bacteria. 

 The air, with the possible exception of that over large bodies 

 of water and in high altitudes, contain varying numbers of 

 bacteria and many species. No family of plants compares 

 with the bacteria in importance. 



Points of Resemblance to Other Forms of Life. The 

 following facts will serve to give an idea of the general points 

 of resemblance of the bacteria to the low plants and animals. 

 It will be seen that they resemble the known plants more 

 closely than the animals, and, consequently, are placed in the 

 lowest order of this kindgom. 



i. In some species of bacteria a thin, limiting membrane, 

 which is related to cellulose or hemicellulose, chemically, is 

 present, and in this particular they resemble plant cells. 

 However, recent investigations have shown that the cell wall 



