64 



EXPERIMENTS IN BLUEBERRY CULTURE. 



McNab's conclusion that manure, while beneficial in small quan- 

 tities, should be used with caution or not at all agrees with the 

 conclusion reached from these blueberry experiments. On page 18 

 of this paper is described the disastrous results of the heavy manur- 

 ing of blueberry plants, and in view of the fact that the blueberry 

 makes satisfactory' growth without manure and that we are not 

 sufficiently informed of the exact conditions under which manure 

 may become injurious, the use of even small amounts for blueberries 

 is not now recommended. 



A suggestion may be made, however, as to a possible reason for the 

 injury of blueberry plants by manure. In the glass-pot experiment 

 described on page 18, in which plants grown in a mixture containing 

 half as much manure as peat made exceptionally good growth at first 

 but soon died, the death of the plants was preceded by a rotting of 

 the roots. Now, manure is alive with myriads of bacteria, while peat 

 contains few. An examination of the two made by Mr. Karl F. Kel- 

 lerman, from samples taken from the kalmia peat and the cow manure 

 used in these experiments, showed 2,500 bacteria per plate in the 



't'lG. 26. — Spores of a supposedly injurious fungus in the epidermal cells of blueberry roots. 



(Enlarged 600 diameters.) 



manure and TO to 150 in the rotted peat, each plate representing 

 0.0004 of a gram of material. The bacteria in the peat were chiefly 

 of two species, while the manure contained many. It is a reasonable 

 supposition that the rotting of the blueberry roots may have been 

 caused or aided b}'^ the bacteria in the manure or by some of the 

 fungi with which manure is also abundantly charged. In mixtures 

 like those recommended by McXab, however, containing much peat 

 and little manure, the injurious bacteria and fungi in the manure may 

 have been killed or held in check by the acids that exist in the peat 

 and keep such organisms in control. If experiments show this theory 

 to be correct, the application of manure to blueberries may then be 

 made intelligently. 



In this connection it may be well to call attention to a peculiar spore 

 found in the roots of feeble blueberry plants grown in unfavorable 

 soils, such as the limed peat and the claj^ey loam described on pages 

 23 and 24, and mixtures containing a large proportion of manure. In 

 some of the epidermal cells of the rootlets were found large spherical 

 bodies, as illustrated in figure 26. They usually occurred singly, 



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