260 AGEICULTUEAL AND INDUSTRIAL BACTERIOLOGY 



task of taking up plant food from the soil and elaborating 

 it for the use of the plant is largely given over to organ- 

 isms growing in the tuberous or nodular roots. Sufficient 

 work has not been done with most of these plants to prove 

 conclusively that the primary function of the mold is to fix 

 atmospheric nitrogen. There is some evidence pointing to 

 this as a fact for certain forms such as the alder, while 

 experiments upon New Jersey tea did not lead to the same 

 conclusion. Apparently there is a condition of symbiosis. 

 The exact benefit reaped by the plant has not been deter- 

 mined with certainty. 



The roots of many trees, and particularly plants growing 

 in bogs and swampy places, are covered with the mycelium 

 of a fungus or so-called ectotrophic mycorrhiza. In certain 

 groups of plants, such as those belonging to the genus Vac- 

 cinium, which includes the huckleberries, blueberries and 

 cranberries, practically no growth will occur, at least nor- 

 mal development will not take place unless the fungi are 

 present upon the roots. In other cases it is apparently 

 true that the mycorrhiza is largely parasitic and more harm 

 is done than good. Certain of the toadstools and mush- 

 rooms which appear in woods are of this character and the 

 hyphse may be traced from the base of the fruiting body to 

 the tip of the tree roots. 



In summary, it may be concluded that many plants not 

 belonging to the group of legumes depend, in part at least, 

 upon the activity of molds growing in their roots or in root 

 nodules, for their best development. It is not at all improb- 

 able that in some cases nitrogen is fixed and furnished to 

 the growing plant by these organisms, but adequate proof 

 has not been brought forward in most cases. 



Nitrogen Fixation by Nonsymbiotic Bacteria. It has been 

 abundantly demonstrated that there are several, probably 

 many, kinds of bacteria living in the soil not in symbiosis 

 with higher plants, which are capable, under certain condi- 



