20 BOTANICAL GAZETTE {JULY 
The organisms show a marked interdependence between them- 
selves; one set of bacteria prepares a medium for another out of 
an unfavorable substratum, and this paves the way for others to 
continue the destruction. Signs are not lacking, however, of 
relative indifference and even antagonism among the organisms, 
resulting in products which retard and inhibit further bacterial 
growth and disintegration processes. 
A certain proportion of bacteria in these soils has the special 
ability to produce substances, perhaps unassimilable, certainly 
injurious to all but indigenous plants. In a peat substratum the 
percentage of bacteria aiding in the production of deleterious 
substances such as reducing bodies, gases, indol, and other 
fermentation products varies with the season of the year, but 
especially with the advance of the vegetation toward the closed 
deciduous forest formation. These bodies constitute the unsanitary 
conditions in soils, the negative factor which limits the rate at 
which the splitting up of organic compounds into ammonia and 
other assimilable substances proceeds. They are the character- 
istic symptoms of a diseased, sterile soil. The greater oxidation 
in the productive peat soil is due to the activity of a different set 
of bacterial organisms. The rédle which microorganisms play 
in the soil points, therefore, to the fact that among other things 
a considerable relation exists between the processes of disintegra- 
tion of organic material and the succession of plant formations in 
bogs and marshes, and in peat soil under cultivation. 
Each plant formation has its own bacterial flora maintaining 
a physiologically balanced condition in the soil. The substratum 
of each plant formation is an ever varying medium, the seat of 
physical, chemical, and vital activities which directly and indirectly 
influence its relative fertility and the character of the surface 
flora. Varying with the power of multiplication and metabolic 
activity is the quantity of the products of decomposition consti- 
tuting a toxic, physiologically arid habitat at one phase, and an 
available supply of nutrients to plants at another stage of the 
process. Acidity, toxicity, and reduction action represent merely 
a stage in the decomposition of organic matter. In the natural 
successions which ensue, each plant association augments the 
