SINGLE-CELLED PLANTS AND COLONIES. 



II 



become so different that they are now known as fission -fungi, 

 and popularly as bacteria, bacilli, microbes, germs, etc. 

 These plants, probably the descendants of common ancestors 

 with the fission-alga^, are the smallest known organisms 

 (figs. 1 6, 17). The diameter of many sorts does not 



V 



* • 



a 3 



00 o§ ~9~ 



e»*g!3fe 



Fig. 16. — Various bacteria, a, Micrococcus, the " blood-portent " ; 6, zoogloea form 

 of the same ; c, Bacterium aceti, the ferment of vinegar ; d, Sarcina, a harmless 

 parasite of the human intestine, a, 6, magnified 300 diam.; c, 2000 diam.; d, 800 

 diam. — After Kerner. 



exceed .0005 of a millimeter. That would allow 175 to 

 lie side by side upon the edge of the paper on which this 

 book is printed. In many the successive divisions are 

 parallel, in others they divide the cells in two planes, and in 

 others again in three. The cells, when they divide, separate 

 readily, in most sorts never cohering at all, but living as 

 independent cells as soon as produced. Other sorts remain 

 connected into two- to several-celled chains, sheet, or packets 

 {a, d, fig. 16). A few have their cells firmly coherent into 



