l6o BACTERIA IN RELATION TO PLANT DISEASES. 



Streptococcus Billroth. 



Cells globose and without organs of motion. Division in only one direction of 

 space. When the cells remain united after division, moniliform chains are produced, 

 or diplococcus forms, but the latter also occur in other genera of Coccaceae. Doubtful 

 if any spore formation. 

 Micrococcus (Hallier) Cohn. 



Cells globose in a free state. Division in two directions of space without previous 

 elongation of cell. No organs of motion. Endospore formation not positively demon- 

 strated and probably wanting. When the cells remain together after division Meris- 

 mopaedia-like plates may be formed, in which case the contiguous cell-walls may be 

 flattened. 

 Sarcina Goodsir. 



Cells globose, in a free state. Division in three directions perpendicular to each 

 other. No organs of motion. Spore formation doubtful. If the cells remain united 

 after division, bale-like constricted packetsare formed ; frequently these do not appear, 

 as the nutrient medium has the greatest influence on the form of the cell-unions. 



Planococcus Migula. 



Cells globose but usually adhering in twos or fours with points of contact flat- 

 tened. Division in two directions of space, as in Micrococcus. Motile by means of 

 one or two long, wavy -bent flagella. Spore formation unknown. 



Planosarcina Migula. 



Free cells globose. Division in three directions of space, as in Sarcina. Motile 

 by means of long or short flagella. Apparently only one flagellum to each cell. No 

 endospores. Usually the cells remain united after division as diplococci or tetracocci, 

 but seldom in the form of packets. 



2. Family BACTERIACEAE. 



Cells longer or shorter cylindric, straight, or at least never spirally twisted. 

 Division in one direction only, viz, perpendicular to long axis, and only after a pre- 

 liminary elongation of the rod. In some species the rods separate early; in others 

 they remain united for a considerable time as longer or shorter threads. A single cell, 

 so far as known, does not immediately break up into two daughter cells when the 

 first septum is formed, but remains as a single rod until additional septa are laid down. 

 In some species the cells may be very short, so as to superficially resemble Strepto- 

 cocci, but an exact study of the cell-division enables one to distinguish with certainty. 



Bacterium Ehrenberg (char, emend.). 



Cells cylindric, longer or shorter, often forming threads of considerable length. 

 Without organs of motion. Endospore formation occurs in many species, but appears 

 to be entirely wanting in others. In many they may yet be discovered when the 

 organisms are exposed to suitable environments. 



Bacillus Cohn (char, emend.). 



Cells straight, rod-shaped to ovoid, longer or shorter, sometimes united into quite 

 long threads. Motile by means of wavy -bent flagella which are scattered over the whole 

 body. Endospore formation frequent. In most species motility occurs only during a 

 definite period of development, which is very brief in some species and very long 

 in others. 

 Pseudomonas Migula. 



Cells cylindric, shorter or longer, sometimes forming threads. Motile by means 

 of polar flagella. The number of flagella on a pole varies from i to 10 ; most frequently 

 it is i , or 3 to 6. Endospore formation certainly occurs in some sorts, but is rare. 



