PURE CULTURE STUDY OF SOIL BACTERIA 57 



bacteria to be a more definite characteristic. The form of growth of the 

 various organisms is also of important diagnostic value. 



As to the various physiological characteristics, some, like liquefaction 

 of gelation, nitrate reduction 13 and chromogenesis, are of considerable 

 diagnostic value; others, like diastatic power, fermentation of sugars, 

 indol formation, action on milk, give rather inconsistant results. 



Although the morphological characters of the bacteria should be uti- 

 lized in a scientific system of classification, the soil bacteria lend them- 

 selves readily to a general classification based upon their physiological 

 activities. Such a system is suggested here for the purpose of grouping 

 the bacteria according to the important soil processes in which they 

 take an active part, utilizing the more systematic classification for the 

 discussion of the specific organisms. 



Life cycles of bacteria. According to Lohnis, bacteria live alternately 

 in an organized and in an amorphous or "symplastic" stage. In the 

 latter stage the living matter which has been previously enclosed in the 

 separate cell, undergoes a thorough mixing either by a complete dis- 

 integration of the cell wall and cell contents or by a "melting together" 

 of the contents of many cells which leave their empty cell walls behind 

 them; it seems to be formed both of the vegetative and reproductive 

 cells; this process is similar to autolysis, without the destruction of the 

 living substance. The symplasm may undergo amoeboid changes or 

 become encapsulated, giving spherical macrocysts. In the process of 

 formation of new individual cells from the symplasm, "regenerative 

 units" are first visible, which increase in size becoming either directly 

 vegetative cells or "regenerative bodies." The latter become, by 

 germination and stretching, normal cells or return temporarily into the 

 symplastic stage. 



In addition to symplasm formation, two or more individual cells may 

 unite directly (conjunction). All bacteria multiply not only by fission 

 but also by the formation of gonidia, which first become regenerative 

 bodies or exospores. The gonidia may either grow directly into full 

 cells or enter the symplastic stage. Thread-like branching forms may 

 also be produced from the symplasm. The life cycles of each species 

 of bacteria is composed of several sub-cycles showing wide morphologi- 

 cal and physiological differences. They are connected with each other 

 by the symplastic stage (Nos. 47, 48, PL IX) . However, some investi- 



" Breed, R. S. The standard method of determining nitrate reduction. 

 Science, N. S. 41: 661. 1914. 



