292 REpoRT OF THE BOTANICAL DEPARTMENT OF THE 
described in an earlier bulletin* of the same station. A Cyto- 
spora was found on the dead bark and considered a parasite. 
To show that the earliest observations on winter-killing of 
apple-tree roots are ancient, J. Craig® quotes instances from 
horticultural society reports of Minnesota, Iowa and Wiscon- 
sin dating back to the early seventies. In these reports it is 
held that bare ground during severe winters permits root-in- 
jury and that mulching is a preventive. Craig observed that 
the basal portions of the upper roots, even of old trees, were 
severely injured during the winter of 1898-9. The region of 
greatest injury was found on the stock (near the ground line) 
from the base of the scion downward even to the depth of 10 to > 
12 inches; below this injured girdle the roots were unaffected. 
Slight injury is said to have been shown by the discolored cam- 
bium and severer effect by the disorganization of the inner bark. 
Seedling roots were more often injured than scion roots on 
root-grafted trees. In fact it seemed that the trees escaping 
destruction were generally found to be dependent on a scion 
root system, though surface protection is thought to be the 
more important factor. Trees 5-15 years old were least in- 
jured and orchards on south slopes or on loam soils were less 
affected than those on north slopes or sandy soil. It is stated 
that fruit growers are agreed that severe, long, cold periods 
and unprotected ground are the primary causes of root injury, 
but that they differ as to the relation the amount of soil-mois- 
ture has to this injury. Some hold that a dry soil is conducive 
to winter-killing of roots and others that a wet autumn pre- 
ceded by a drought is the decisive factor when followed by a 
severe winter. According to the latter theory, which is thought 
plausible, freezing of the excessive water in the roots causes 
mechanical injury to the tissues. 
Ben Davis is considered less hardy than Pointed Pipka, but 
varietal hardiness is said to be unable to prevent injury when 
the ground is bare and the temperature very low. The hardi- 
‘N. Y. Agrl. Expt. Sta. Bul. 167, p. 286. 1899. 
*> Observations and suggestions on the root-killing of fruit trees. Iowa 
Agr]. Expt. Sta. Bul. 44. 1900. 
