48 EXPERIMENTS IN BLUEBERRY CULTURE. 



(18) From tke evidence at hand the presumption is that the mycorrhizal 



FUNGUS of the SWAMP BLUEBERRY TRANSFORMS THE NONAVAILABLE NITRO- 

 GEN OF PEATY SOILS INTO A FORM OF NITROGEN AVAILABLE FOR THE NOUR- 

 ISHMENT OF THE BLUEBERRY PLANT. 



It is a well-established principle of plant physiology that (with the 

 possible exception of a few bacteria) those plants which contain no 

 chlorophyll, the green coloring matter of leaves, are unable to grow 

 Avith mineral nutrients alone, since they are unable to manufacture 

 their own carbohydrates. Plants without chlorophyll, including the 

 fungi, are dependent for the fundamental part of their nourishment 

 on the starch or other related carbohydrates originally elaborated 

 from carbon dioxid and water by the chlorophyll-bearing plants. 

 They also differ from the higher plants in being able to supply their 

 nitrogen requirements directly from organic nitrogen compounds. 



Fungi may be directly parasitic on a chlorophyll-bearing plant, as 

 in the case of the mildew fungus of rose leaves, or they may grow on 

 substances derived from chlorophyll-bearing plants, such as bread 

 or jelly. 



Fungi are particularly^ abundant in the decaying vegetable matter 

 forming the leaf litter of a forest, even though this litter may be 

 distinctly acid in its chemical reaction. They are known, indeed, 

 to grow luxuriantly on vegetable remains containing no nitrates and 

 of such acidity that nitrification, or the conversion of the humus 

 nitrogen into nitrates by means of bacteria, can not take place. 



That the mycorrhizal fungi, like other fungi, are able to extract 

 nitrogenous food from the nonnitrified organic matter with which 

 their external portions are in contact is a reasonable supposition. It 

 is furthermore a reasonable supposition that the blueberry plant is 

 able to absorb nitrogenous -material from the internal portion of its 

 mycorrhiza ; for we know that the clover plant is able to absorb nitro- 

 gen under essentially the same conditions from the nitrogen-fixing 

 bacteria growing in its root tubercles. 



To establish by direct experiment the ability of the mycorrhizal 

 fungus of the blueberry to act it. accordance with the supposition 

 outlined above, the fungus should be separated from the plant and 

 grown by itself in suitable nutrient media. Preliminary trials were 

 made to isolate the fungus, but without success, and a lack of time 

 has prevented thus far the pursuit of that branch of the experiments. 



(19) It is POSSIBLE that THE MYCORRHIZAL FUNGUS OF THE SWAMP BLUEBERRY 



TRANSFORMS THE FREE NITROGEN OF THE ATMOSPHERE INTO A FORM OF 

 NITROGEN SUITED TO THE USE OF THE BLUEBERRY PLANT. 



The fact of the fixation of atmospheric nitrogen by the bacteria 

 inhabiting the root tubercles of clovers is now well known, and we 

 are able to understand how the abundant nitrogen of the air, unavail- 



193 



