EFFECT OF PUEE PEAT IX PLUNGED POTS. 69 



are very liable to death from dryness. When the pot is plunged in 

 sand and the sand is kept moist these rootlets can* not die from 

 drought. They keep on growing until, in the case of vigorous plants, 

 when the earth ball is knocked from the pot, the soil can not be seen 

 because of the dense mat of live roots that line the pot. The same 

 thick mass of live roots was developed in a series of 1907 seedlings 

 carried over the Avinter of 1908-9 in the greenhouse in pots plunged 

 in sphagnum. When the pot is surrounded by the moist plunging 

 material these roots continue to luxuriate for months longer than 

 they otherwise would. They evidently find the aeration conditions, 

 as well as the moisture conditions, at the wall of the pot very satis- 

 factor}^, for the development of roots there is far greater than within 

 the ball itself. 



The highly efficient aeration at the wall of plunged pots may 

 explain one use of soils in which the results of the present investiga- 

 tions do not agree with the practice of the old heath growers. In 

 one culture of 25 plants the soil used in the first potting was pure 

 rotted kalmia peat rubbed through a quarter-inch screen. This first 

 potting, in 4-inch pots, was done on March 20. 1909. The repotting, 

 in (i-inch pots, was done on May 22, 1909, in the same kind of soil, 

 pure coarsely sifted kalmia peat. These j^lants grew to be the 

 largest of any of the seedlings of 1908, their average height at the 

 close of the season being 20.5 inches. The three plants shown in 

 Plate IX, all over 24 inches in height and one of them 27 inches. 

 ^^ ere from this culture. 



The use of pure peat was not advocated by the old heath growers. 

 McXab recommended a mixture of 4 or 5 parts of peat, by bulk, to 

 1 of sand, and an even larger proportion of sand, 2 parts out of 5, 

 has been reconnnended by Dawson for blueberries. When the pots 

 are not plunged and do not therefore have the advantage of the 

 superb aeration conditions found at the wall of the pot when sur- 

 rounded by moist sand, it is probable that the presence of consider- 

 able sand in the soil is necessary to secure adequate aeration of the 

 interior of the earth ball, for unless the pot is plunged most of the 

 rootlets that lie against the sides of the pot will be killed and the 

 plant nuist rely for its chief nourishment on the roots in the interior 

 of the ball. 



That the necessity for interior aer-ation in the pots is great in the 

 case of heaths, if the plants are not plunged or are not frequently 

 repotted, is shown by a peculiai- and interesting cultural practice 

 long tried and highly reconnnended by McNab. This practice is 

 the distribution of broken crocks or pieces of sandstone through the 

 soil at the time of I'epotting. He found by experience that the prac- 

 tice was highly advantageous to the plants, and although he did not 

 directly explain his success in such a way, there is little doubt that 



193 



