564 



ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 



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- 

 tegi'ate 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- 



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 foi-mer 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, e. 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 



