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discovered that certain forms of bacteria 
are capable of fixing free nitrogen. These 
are found most often on the leguminous 
plants where they collect in nodules. The 
physical action of these colonies is to 
break up the organic matter in the soil 
and, through the action of certain acid 
by-products, the inorganic as well. They 
thus render soluble the various elements 
in the soil which are necessary for plant 
food. In addition they seem capable of 
utilizing free nitrogen from the air in 
such a way as to increase the quantity 
of this element in the soil. Thus the 
nitrogenous or leguminous plants such 
as clover, vetch, alfalfa, beans, peas, 
etc., tend to improve the quality of a 
soil which is in need of nitrogen. 
Prof. H. Marshall Ward, University of 
Cambridge, says: 
“These bacteria can build up organic 
matter from purely mineral sources by 
assimilating carbon from carbon-dioxide 
in the dark, and by obtaining their nitro- 
gen from ammonia. The energy liberated 
during the oxidation of the nitrogen is 
regarded as splitting the carbon-dioxide 
molecule—in green plants, this work is 
done by the solar rays. Since the supply 
of free oxygen is dependent on the ac- 
tivity of green plants, the process is indi- 
rectly dependent on energy derived from 
the sun, but it is nevertheless an astound- 
ing process and outside the limits of our 
previous generalizations.” 
Important results often occur, in the 
fact that these bacteria tend to disin- 
tegrate stone, rot sand particles, rust iron 
and copper, rendering their particles 
soluble. 
Saprophytic and Parasitic Bacteria 
Saprophytic bacteria are those which 
live in dead matter whether animal or 
vegetable. They are associated with 
most decomposing processes. 
Prof. A. C. Abbott, of the University of 
Pennsylvania, says: 
“The saprophytic group comprehends 
many species used in the fine arts and 
industries—such for instance as those 
concerned in the production of certain or- 
ganic acids; those employed in the manu- 
ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 
facture of indigo by the fermentation pro- 
cess and in the preparation of hemp; and 
in those used in the manufacture of 
cheese and butter In the study of this 
large group, one constantly encounters 
other species presenting most engaging 
characteristics. Some of these varieties 
have the property of producing, during 
the course of their growth, pigments of 
great beauty—brilliant reds, delicate 
pinks, rich purples, yellows ranging from 
the palest lemon to the deepest orange. 
In another group, we meet with species 
having the emission of light as their most 
singular peculiarity When growing, 
these forms glow with a peculiar phos. 
phorescence, and it is significant to note 
that these luminous varieties have been 
most frequently encountered in the sea, 
and upon articles from the sea. The 
evil odors of putrefaction are the results 
of saprophytic bacterial development. 
“In the parasitic group of bacteria, we 
encounter those species that exist always 
at the expense of a living host, either 
animal or vegetable, and in doing so not 
only appropriate materials necessary to 
life, but give off in return waste products 
that may act as direct poisons to the host. 
Fortunately this is a much smaller group 
than the saprophytic. In no particulars, 
save for their ability to exist at the ex- 
pense of a living host and cause disease, 
are the disease producing bacteria dis- 
tinguishable from the innocent varieties. 
The essential difference between the 
disease producing and the innocent bac- 
teria, is that the former possess as their 
most striking physiological peculiarity, 
the power of elaborating toxins or pois- 
ons, that have a direct effect, or destruc- 
tive action upon the tissue of their host.” 
H. Marshall Ward says: “A long list 
of plant diseases has of late years been 
attributed to bacterial action. Some, @. g. 
the Sereh disease of the sugar cane, the 
Slime fluxes in oaks and other trees, are 
not only very doubtful cases, in which 
yeast and other organisms such as fungi 
play their parts, but it may be regarded 
as extremely improbable that the bacteria 
are the primary agents at all. They are 
doubtless saprophytic forms, that have 
