116 Principles of Plant Culture. 
Aside from the death of tender plants by cold, more or 
less hardy species suffer injury in a variety of ways, of 
which the following are examples: 
192. Destruction of Terminal Buds by Cold. In 
plants which do not mature their terminal buds in autumn, 
as the raspberry, sumac, grape, etc., destruction of the tips 
of growing shoots by frost is a regular occurrence, in 
climates of severe winters. The distance which the shoots 
are killed back, depends upon the succulency of the growth, 
the coldness of the winter, and the natural power of the plant 
to endure cold. Plants thus affected are not always to be 
regarded as tender, since they grow wild in climates of very 
severe winters. 
193. The Darkening of the Wood (black-heart) of 
certain trees, as the pear, in climates of severe winters, 
appears to be a chemical effect of the cold. It begins at the 
center of the stem, and in extreme cases, may extend clear 
to the cambium, when the bark ceases to adhere, and the 
tree or branch thus affected dies. In stone fruits, this 
trouble is often accompanied by a flow of gum. If the 
coloring of the wood does not extend to the cambium, the 
tree or branch may survive, but the first season’s growth 
thereafter is generally feeble and the fruit or the seed crop 
often fails. During the second season, healthy growth may 
be resumed, but the heart is rarely or never restored to its 
normal color. Black-heart often results from other causes 
than cold, as from bacteria that gain access to the heart- 
wood through wounds (419). 
Other chemical changes result from cold, as the sweeten- 
ing of potato tubers when chilled, the removal of astringency 
from the wild grape and persimmon, and the heightening of 
the flavor of the parsnip. 
