294 Missouri Agr. Exp. Sta. Research Bulletin No. 8 



is not grown commercially in as severe climates as those in which 

 apples are sometimes grown, yet killing of roots of peach trees is 

 observed in fairly important commercial peach districts.^ 



Macoun^ reports that killing of apple roots is fairly common 

 in the northern portion of the apple growing section and says that 

 the root killing they have had in Canada has been when apples were 

 worked on seedlings of southern forms, and that since the crab has 

 been used as stock, the killing has been much less. 



Emerson^ at the Nebraska Experiment Station planted apple 

 trees in boxes two feet square and eighteen inches deep, each box hav- 

 ing twenty-five young roots. The boxes were left out of doors 

 about the middle of December, the soil having different percentages 

 of moisture. The trees were examined on February 25. In an un- 

 protected box containing 10.4 per cent of moisture, twenty roots 

 were killed, only five remaining uninjured. Another unprotected 

 box containing 15.2 per cent of moisture had nineteen killed and six 

 injured. In a box containing 19.8 per cent of moisture, three were 

 killed, ten injured and twelve uninjured. A box covered with straw 

 mulch and containing 16 per cent of moisture had none of the roots 

 killed, and only seven injured. A box covered occasionally with snow 

 and containing 15.8 per cent of moisture had seven dead, eight in- 

 jured and ten uninjured. No roots were injured in a box stored in 

 a cool, dry cave, though it contained but 10 per cent of moisture. 

 It is shown from this experiment that the low moisture content in 

 itself did not do the harm, but the low moisture associated with low 

 temperature. It does not seem, however, that one is justified in 

 concluding, as Macoun apparently does, that plants at any given 

 temperature kill worse in media with as small as 10 per cent of mois- 

 ture than in media with 20 per cent of moisture. From experience 

 here it would seem likely that the reverse is true. Careful tempera- 

 ture records would probably indicate that the temperature was lower 

 in the boxes containing the smaller moisture content, and a dry soil 

 will freeze more deeply than will a moist soil. Thus a mulch or sod 

 or cover crop that tends to prevent evaporation from the soil will 

 prevent its freezing so deeply and thus prevent injury to the roots 

 by keeping the temperature higher. 



Craig^ studied root killing in Iowa for the winter of 1898-99. 

 The injury was worst in light dry soils not protected by a cover crop 



iStone. Mass. (Hatch) Exp. Sta. Rpt. 1911, p. 66. (BibL No. 107). Green, W. J. and 

 Ballou, F. H., Ohio Agr. Exp. Sta. Bui. 157, 1894. (Bibl. No. 48). 

 ^Canada Exp. Farms, Rpt. 1907-8, pp. 110-16. (Bibl. No. 68). 

 sNebraslca Agr. Exp. Sta. Bui. 79. 1903.- (Bibl. No. 33). 

 *Iowa Agr. Exp. Sta. Bui. 44, 1900. (Bibl. No. 25). 



