BACTERIA IN THE INDUSTRIES l6l 



the plants reenter the soil, enriching it. Pure cultures of these bacteria 

 have been in use for some time (over thirty years) for the purpose of 

 increasing the crop yield in virgin soils and in soils deficient in nitro- 

 genous compounds. These socalled vest pocket fertilizers are extensively 

 manufactured in the United States, in Canada and in other agricultural 

 countries, some of them bearing special fanciful trade names. 



The biological and mutualistic relationship between the three groups of 

 bacteria and the crop plants is very definite. The bacteria of group one 

 may be looked upon as the pioneers, preparing the way for groups two 

 and three. It is they which prepare the raw and as yet wholly unavailable 

 food materials for the use of growing crop plants. That is, they render 

 available to the crop plant, either directly or indirectly, the as yet un- 

 available or locked foods of the soil. It is they which must contend with 

 the various objectionable organisms found in the soil, such as the protozoa 

 and the molds. The bacteria of group two are more favored by virtue of 

 their position upon and near the rootlets and the root hairs of plants where 

 the moisture supply as well as chemical food materials are more constant. 

 Unless bacteria of group one perform their work properly, bacteria of 

 group two cannot in turn perform their work and a crop failure is the 

 result. Bacteria of group two may be looked upon as the go betweens of 

 the crop plants and the bacteria of group one. The position as well as 

 the work of the bacteria of group three is unique. They receive unusual 

 protection by virtue of their position within the root nodules and they 

 deal directly with the plants with which they are thus closely associated, 

 having no biological relationship to the bacteria of either group one or of 

 group two. They constitute the transfer agents between the free nitrogen 

 of the air and the host plants with which they are associated. It must 

 however be stated that many bacteria of group two, as for example the 

 Azotobacter group (includingal so other organisms of the soil, such as 

 higher fungi and many of the algae) have the power of assimilating, for 

 the use of the crop plants, the free nitrogen of the air; however free 

 nitrogen assimilation is the special function of the bacteria of group three. 



The question as to which of the three groups of bacteria is the most im- 

 portant in crop growing, might be debated; however, all scientists are 

 agreed that the three groups are of the greatest importance in agriculture. 

 Good crops might be matured in soils having a paucity of bacteria of group 

 one provided the necessary chemical materials were supplied artificially. 

 Again, fair crops might be matured in soils having a paucity of bacteria 

 belonging to group two, provided certain other, directly available, chemical 

 fertilizers were supplied; and it is known that members of the bean family 

 will grow to maturity and yield fairly well without the root nodule bacteria, 



provided the proper nitrogen bearing food materials are supplied. It has 

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