24 EXPERIMENTS IN BLUEBERRY CULTURE. 



(4) The swamp blueberry does not thrive in a heavy clay soil. 



In its natural geographic distribution the blueberry shows an 

 aversion to clay soils. Its favorite situations are swamps, sandy 

 lands, or porous, often gravelly loams. When a blueberry plant 

 grows upon a clay soil it is usually found that its finer feeding roots 

 rest in a layer of half-rotted vegetable matter overlying the clay. 

 Often in such situations the dense covering of interwoven rootlets 

 and dark peatlike soil may be ripped from the surface in a layer 

 little thicker than a door mat and of much the same texture. The 

 roots of the blueberry do not penetrate freely into the underlying clay. 



In greenhouse cultures the blueberry shows the same aversion to 

 clay soils. Various series of blueberry seedlings were potted on May 

 26, 1908, in different soils in ordinary large drinking glasses. For 

 one set of six plants a stiff clayey soil was used, such as is common 

 in the neighborhood of Washington, D. C. The soil in the glass was 

 mulched to the depth of nearly an inch with half-rotted leaves. In 

 another six glasses were set six similar plants in a peat soil, the sur- 

 face mulched in the same way as the others. 



In other experiments with this clay soil in earthen pots, the growth 

 of the plants had always been poor. The present experiment was no 

 exception. But the feature of greatest interest was the behavior of 

 the roots. Plate I, from photographs taken October 5, 1908, shows 

 the root systems of typical plants in the two soils. In the clay soil 

 almost no root development took place, and in the illustration no 

 roots are visible. The interrupted black lines in the clay are tunnels 

 made by larvae or other animals. In the moist leaf mulch covering 

 the clay, however, the plant developed its roots extensively. Some of 

 the plants, probably because they were set too deeply in the clay 

 when the potting was done, failed to send their roots up into the 

 mulch, and such plants were much inferior in their growth to those 

 that found the rotted leaves. In the other glass is shown the normal 

 root growth of a blueberry in a soil suited to it. 



(5) The swamp blueberry does not thrive in a thoroughly decomposed leaf 



mold, such as has a neutral reaction. 



It had been found in earlier experiments that certain soils com- 

 posed in part of imperfectly rotted oak leaves were good for growing 

 blueberries. On the supposition that the more thoroughl}^ rotted this 

 material was the better suited it would be for blueberry growing, a 

 quantity of old leaf mold was secured for an experiment. The mold 

 was black, mellow, and of fine texture. The mixed oak and maple 

 leaves from which it was derived had been rotting for about five 

 years, until all evidences of leaf structure had disappeared. It had 

 the same appearance as the black vegetable mold that forms in rich 

 woods where trilliums, spring beauty, and bloodroot delight to grow. 



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