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THE NATIONAL GEOGRAPHIC MAGAZINE 



plants. The cells in which it is found 

 are not swollen nor distorted, nor do 

 their contents collapse or show any of 

 the other effects usually produced by 

 injurious fungi. There is no indication 

 that the fungus is in any way obnoxious 

 to the plant. On the contrary, the uni- 

 formity with which it has been found to 

 occur on healthy plants and its frequent 

 absence or scarcity on sickly plants are 

 at once suggestive of a mutually bene- 

 ficial relationship. 



It is well known that fungi differ 

 from the higher plants in being able to 

 take their required nitrogen directly 

 from organic nitrogen compounds. They 

 do not require that the nitrogen they 

 consume shall be in the form of nitrates. 

 Fungi are particularly abundant in the 

 decaying vegetable matter forming the 

 leaf litter of a forest, though this litter 

 may be distinctly acid in its chemical 

 reaction. Indeed, they grow luxuriantly 

 on vegetable remains containing no ni- 

 trates and of such acidity that the con- 

 version of humus nitrogen into nitrates 

 by means of bacteria cannot take place. 



As a reasonable explanation of the 

 phenomena presented in the peculiar life 

 history of the blueberry, the conclusion 

 has been reached that the root fungus 

 extracts nitrogenous food from the non- 

 nitrified acid organic matter with which 

 it comes in contact and changes it into 

 some chemical form in which the blue- 

 berry plant can make use of it. Such a 

 transformation is analogous to that al- 

 ready well known to occur in the root 

 tubercles of leguminous plants. It is 

 quite within the range of possibility that 

 mycorhizas, as these structures are called, 

 consisting of a root and its symbiotic 

 fungus, will ultimately be proved to 

 have a very high place in agriculture as 

 nitrogen purveyors, second only in im- 

 portance to these same leguminous tuber- 

 cles. 



BLUEBERRIES THRIVE ONLY IN VERY ACID 



SOIL 



The writer's experiments with blue- 

 be rries, which extended over a period 

 of four years, covered a great diversity 

 of soil mixtures, nutrient solutions, meth- 



ods of potting, amount of shade, and 

 day and night temperatures. Glass pots 

 were much used, to facilitate the study 

 of the roots. A hole was bored in the 

 bottom to give the necessary drainage, 

 and the glass was darkened by a remov- 

 able cuff of opaque gray blotting paper. 

 The use of these glass pots resulted in 

 an intimate knowledge of the behavior 

 of blueberry roots under different soil 

 conditions, which could not have been 

 secured in any other way and which 

 was essential to the correct interpreta- 

 tion of the experiments. 



In a rich garden soil in which alfalfa 

 seedlings and rose-cuttings grew luxuri- 

 antly the blueberry plants stagnated, but 

 in an acid soil the blueberries became 

 large and vigorouo, while roses and al- 

 falfa starved and died. Alfalfa is ex- 

 ceedingly sensitive to acidity and cannot 

 be grown with success in soils that have 

 not a somewhat alkaline reaction. When 

 grown in the humid eastern United 

 • States, alfalfa is rarely successful, ex- 

 cept on calcareous soils, unless the natu- 

 ral acidity of the soil has been neutral- 

 ized by suitable applications of lime. 



Heavy manuring, also, is injurious to 

 the blueberry. Six blueberry seedlings 

 were transplanted into glass pots in a 

 good blueberry soil, and six more seed- 

 lings were potted in the same manner, 

 except that to each two parts of blue- 

 berry soil one part of well-rotted cow 

 manure was added. At first the manured 

 plants appeared, superficially, to be doing 

 better than those not manured, for in the 

 former the production of new leaves and 

 the continued growth of the stem were 

 not interrupted by the potting, while in 

 the plants not manured there was a tem- 

 porary but definite stoppage of stem 

 growth immediately after the potting. 

 The apparent superiority of growth in 

 the manured plants, above ground, con- 

 tinued for about three weeks. Below 

 ground, however, the roots of the two 

 cultures showed directly opposite results. 

 In the plants without manure, new root 

 growth began a few days after potting. 

 At the end of three weeks the develop- 

 ment of an extensive root system was 

 well under way and the plants were 



