AERATION CONDITIONS IN SAND AND PEAT. 37 



nished no appreciable nourislinient and the only essential difference 

 in the two cases was the abundant root aeration afforded by the sand 

 culture. Sand is therefore regarded as having been shown experi- 

 mentally to furnish conditions suitable for soil aeration. 



In all the experiments in which blueberry seedlings were grown in 

 sard cultures suitably acidulated, the root growth was good, even 

 when very little nourishment was given the plant, and when fed with 

 a weakly acid nutrient solution or with peat water the sand-potted 

 plants always made a luxuriant root growtii. 



In their wild state blueberries are especially prevalent on the sandy 

 soils of the Atlantic Coastal I*lain, as well as on sandy plains and i)ine 

 barrens in the inlci'ior. The drainage of such soils is good and their 

 aeration is excellent. 



(11) Aeration conditions satisfactokv kou tuk swamp 1!luebekky akk found 

 in drained emjkous peat. 



Kalmia peat when in the original turfs or mats is full of small 

 roots of oak, kalmia, and other plants. In that condition it is remark- 

 ably porous and w^ell aerated. Pieces of these turfs were used with 

 great success in the bottoms of pots, in place of crocks, to afford drain- 

 age. For a potting soil, however, kalmia peat can not easily be used 

 until the soil has been shaken from the mass of roots or has been 

 rulibed through a screen. Even in that condition the fragments of 

 leaves and rootlets make the whole mass porous. A ])()t containing 

 pure kalmia peat prepared by such rubbing often remains moist, yet 

 well aerated, for days at a time wnthout watering. This moisture con- 

 dition is due to two remarkable properties of peat, its ability to hold a 

 large amount of water, and the tenacity with which it clings to it. 



Kalmia peat taken from the interior of a stack after it has remained 

 several months under cover ordinarily contains 100 ])er cent of 

 water, comj)uted on the dry weight of the peat. Even with this very 

 high water content a i:)eat soil is in a beautiful condition of tilth, 

 mellow, well aerated, and to the sight and touch apparently only 

 moderately moist. Ordinary loam in a similar condition contains 

 only about 18 per cent of water, and sand about .'^ per cent. When 

 saturated with water the moistui'e content of kalmia peat is about 

 500 i)er cent of its dry weight. 



The ability of peat to retain its moisture depends in part on the 

 gi-adual drying of the superlicial layers and the consequent formation 

 of a nudch, but more i)articularly is it dependent on a certain phys- 

 ical affinity that peat possesses for water. The comparative strength 

 of this water-holding power in different soils may be tested by sub- 

 jecting them to a powerful centrifugal force, which tends to throw 

 the moisture out of the soil. The standard centrifugal force used 

 is a thousand times the force of gravity. The percentage of moisture 



193 



