4 BULLETIN 1477, U. S. DEPARTMENT OF AGRICULTURE 
the tree out of its regular balance of growth and production. An 
occasional excessive pruning may strongly oppose the natural tend- 
encies of growth and prove to be a costly mistake. 
EXPLANATIONS OF TERMS USED 
Training, or the shaping treatment given the young tree, is con- 
sidered somewhat distinct from pruning and is not discussed in this 
bulletin. Unless otherwise stated it is understood that the trees 
under consideration are those of normal vigor, growing in suitable 
soil which is of moderate depth and fertility, given some irrigation, 
making a moderate annual growth, and bearing regular and mod- 
erate crops. 
Heading back, as used here, refers to the cutting back of 1-year- 
old shoots. With some fruit growers heading back is used to mean 
cutting well back into the old wood for the purpose of developing 
a new top of fruiting branches. This is done particularly with 
peaches in some parts of the country, but is rarely practiced in the 
West with plums. 
The terms used to indicate different parts of the tree are presumed 
to be self-explanatory. 
Framework branches denote those which grow from the trunk of 
the tree, and secondary branches those which grow from the frame- 
work branches. Next are the fruiting branches, and on these are 
twigs, spurlike twigs, and spurs (pi. 2, A). A spurlike twig is a 
growth which, because of unfavorable conditions, has failed to make 
more than a very short development and resembles a spur more than 
a twig. Such twigs are often unbranched or the branches are short 
and spurlike. W^hen favorable growing conditions recur a normal 
twig grows from the terminal bud. Twiglike spurs are normal 
spurs which branch but little, if any, but become long by the annual 
growth from the terminal bud (see pi. 9, D). Spur twigs are 
short twigs that grow from vigorous branches or spurs which pro- 
duce lateral spurs and a terminal spur but are not inclined to produce 
new twigs (see pi. 32, C). If twigs do grow from them they 
produce spurs the same as the ones on which they grow. Twigs 
grow from the main wood of a shoot, branch, or twig, but are 
slender and grow to a few inches or more in length. Some twigs 
bjranch more or less freely, and the terminal buds of both the main 
twig and its strongest branches send out a few inches of new 
growth each 3^ear. The weaker lateral branches of twigs often make 
but a short spurlike growth and die after fruiting. When growing 
conditions are unfavorable, many or all twigs are short, and many 
make but a spurlike terminal growth for one or more years or until 
conditions for growth improve. 
GROWING HABITS OF PLUM TREES IN RELATION TO PRUNING 
In training the young tree and in maintaining its shape and vigor 
when in bearing, the pruner should carefully consider the varietal 
characteristics of growth and production, such as the tendency to 
grow erect or spreading, open or compact, to make long or short an- 
nual wood growth, to maintain vegetative vigor, and the inclination 
to produce twigs or spurs. 
