RELATION TO ENVIRONMENT CLASSIFICATION 41 



observed was not a constant one for each genus, but that cocci could 

 be converted into bacilli or spirilla according to environmental con- 

 ditions. It was Cohn 31 who, in 1872, first recognized the constancy 

 of the morphology of bacteria and established, upon morphological 

 basis, a classification which, with minor changes, has been retained 

 until the present day. Such classifications can not, however, be re- 

 garded as anything more than a convenient make-shift pending the 

 day when the finer structure and true biological relations of the 

 various bacteria shall have been more accurately investigated. The 

 scheme most commonly accepted at present is the one given below, 

 proposed by Migula : 32 



Bacteria (Schizomycetes). Fission fungi (chlorophyll free), cell division in 

 one, two, or three directions of space. Many varieties possess power of 

 forming endospores. Whenever motility is present, it is due to flagella, 

 or, more rarely, to undulating membranes. 



FAMILY I. COCCACE^E. Cells in free state spherical. Division in one, two, 



or three directions of space, by which each cell divides into two, four, 



or eight segments, each of which again develops into a sphere. Endo- 



spore formation rare. 

 Genus I. Streptococcus. Cells divide in one direction of space only, for 



which reason, if they remain connected after fission, bead-like chains 



may be formed. No organs of locomotion. 

 Genus II. Micrococcus (Staphylococcus). Cells divide in two directions 



of space, whereby, after fission, tetrad and grape-like clusters may be 



formed. No organs of locomotion. 

 Genus III. Sarcina. Cells divide in three directions of space, whereby, 



after fission, bale-like packets are formed. No organs of .locomotion. 

 Genus IV. Planococcus. Cells divide in two directions of space, as in 



micrococcus, but possess flagella. 

 Genus V. Planosarcina. Cells divide in three directions o space as in 



sarcina, but possess flagella. 



FAMILY II. BACTERIACE^:. Cells long or short, cylindrical, straight, never 

 spiral. Division in one direction of space only, after preliminary 

 elongation of the rods. 



Genus I. Bacterium. Cells without flagella, often with endospores. 



Genus II. Bacillus. Cells with peritrichal flagella, often with endo- 

 spores. 



31 Cohn, "Beitrage zur Biol. d. Pflanzen," Heft 1 u. 2, 1872. 

 82 Migula, " System d. Bakt.," Jena, 1897. 



