326 REPORT OF THE BOTANICAL DEPARTMENT OF THE 
while roots seems more often affected on high, dry land. The 
observations by Nelson in Wyoming and Emerson’s experi- 
ment in Nebraska are illustrations of the latter. But from 
recommendations by Clinton it seems that in Connecticut the 
highlands are to be preferred for orchards. Emerson also ad- 
vised the use of high ground in connection with cover crops 
to induce early maturity. 
My observations seem to indicate that the crowns and roots 
of apple trees were more often injured on rather thin, dry 
Jand. One reason seems to be that the specific heat of dry 
soil is less than that of wet soil, and that therefore its tem- 
perature changes more rapidly and cold penetrates more deeply 
than in wet soil. Sod orchards seem to have been less winter- 
injured on both roots and branches than cultivated ones. Pad- 
dock and others record the same for Sphropsis cankers, and 
it is common knowledge that * fire blight”? occurs more gen- 
erally in cultivated orchards. But in regard to the Crown- 
rot-tvype of winter-injury, it seems that that occurs most 
readily in orchards after the breaking of the sod, though on 
thin land sod cannot always prevent it. From the few cases 
observed it seems that it is not tillage, as such, that induces 
root-injuries, but the change from sod to tillage. Probably 
the unaccustomed amounts of nutrients and moisture avail- 
able to sod trees when they are tilled, or to cultivated trees 
when they are unusually fertilized, stimulate them to excessive 
and late growth which may result in winter-injury. AS sug- 
gested before, soils permitting the formation of deep, extensive 
root-systems seem to enable trees to recover much more readily 
when they have been crown or root-injured. Hartig®* suggests 
that a deep root-system conducts heat upward during frozen 
winters. Oraig and others have also observed that Crown- 
rotted trees generally have their deepest roots unaffected. 
PREVENTIVE MEASURES IN GENERAL. 
The preventive measures generally advised are: Karly, thor- 
ough cultivation, followed by a cover crop in midsummer ; if 

54 Diseases of Trees; p. 283. 
