118 Principles of Plant Culture. 
trees, especially when grafted with short cions (386). With 
very severe freezing, on bare ground, root-killing sometimes 
occurs on soil well supplied with water. The destruction 
of the roots may be complete or only partial. In the latter 
case, the tree, if of a vigorous, hardy variety, may largely 
outgrow the trouble, though complete recovery is rare. 
Treatment that prevents late growth (200, 201), or mulch- 
ing the ground about trees tends to avert root-killing. 
197. Flower-Buds are often Destroyed by Cold while 
other parts of the plant are uninjured. This frequently or- 
curs in the peach, apricot, nectarine and certain species of 
the plum in climates of rather severe winters, especially 
after the buds have been somewhat excited by unseasonable 
warm weather. Flower-buds thus destroyed are dark-col- 
ored at the center. 
198. Flowers are Especially Sensitive to Cold. 
Fruit crops are usually wholly or in part cut off if a slight 
frost occurs during bloom, and in certain fruits, as the apricot 
and some species of the plum, the blossoms sometimes ap- 
pear to be destroyed by a degree of cold that does not 
descend to the freezing point, possibly through interference 
with pollen germination (151). When the freezing is ac- 
companied with snow, however, open flowers may escape 
without harm, probably owing to the slow extraction of the 
frost (190 8). 
199. Low Plants are often Destroyed by Ice, espe- 
cially when the ice layer forms in direct contact with the 
soil about them, and remains for a time after the return of 
warm weather. Snow, of which the top has formed into a 
crust of ice, sometimes acts in the same manner. Winter 
grain and strawberry plants, are often smothered in this 
