8 BULLETIN" 1477, TJ. S. DEPARTMENT OF AGRICULTURE 
ing trees which produce spurs will often lose their vigor earlier 
than those more inclined to produce twigs. Also, the new shoots 
which appear are often well down on the older wood. On the 
upper branches of such trees the fruit as well as wood and leaf 
growth is usually small. Under similar conditions, trees which 
produce twigs instead of spurs are inclined to retain their vigor 
better, although the twigs are not much longer than spurs. If grow- 
ing conditions are favorable, some twig growth will take place at 
the terminals of some of the spurs of the spur-forming varieties, 
even where little or no pruning has been done. 
Trees of varieties which are decidedly inclined to produce twigs 
rather than spurs, of which Giant, Agen, and Italian Prune are 
typical, continue to form new twigs from nodes of 1-year-old wood 
and to extend the terminal growth of twigs throughout the tree 
even where not pruned, if other conditions favor wood growth. 
By cutting back in pruning, the length growth of the twigs is 
greatly increased, and but few of them remain as short spurlike 
twigs, such as are found on unpruned trees. On trees which tend 
to produce twigs, the twigs appear principally at nodes of 1-year- 
old wood, but with trees of the spur-forming groups, any twigs 
which appear are usually the terminal outgrowth of spurs and seldom 
grow from 1-year-old branches unless these branches have been cut 
back. Few twigs are produced on most trees of the latter varieties, 
unless they are cut back in pruning or unless the crop is light. 
With a number of Japanese varieties, many long, slender twigs 
appear as an outgrowth of spurs, if the trees are severely cut back, 
the soil fertile, and moisture plentiful. 
With spur-forming varieties the setting of spurs and their vigor 
and long life should be encouraged. Much toward this end may be 
accomplished in pruning by the thinning or heading back of -branches, 
or both, to suit the needs of the variety and the individual tree. 
With such varieties excessive heading back may result in the loss of 
spurs in the interior of the tree through injury from shade caused 
by the dense new tops or by the outgrowth of spurs and twigs that 
follow such pruning. Too light pruning of such varieties may result 
in but little growth of the framework branches and in small fruit. 
Light pruning of varieties inclined to produce twigs instead of spurs 
may cause but a short growth of twigs and the formation of but few 
new ones. 
The spurs of some Japanese sorts, of which the Apple variety is 
an example, are slender and brittle, and many of those on which 
twigs are being produced are broken during the fruit harvest and 
by strong winds. Spurs of the Japanese variety Formosa and of 
most domestica varieties, which increase in length considerably from 
year to year, become much strengthened as twigs grow from them, 
and they do not break as easily as those which grow slowly and 
remain slender. 
If the vegetative vigor of the spur is low, as is often the case 
with compact trees of some Japanese varieties such as Beauty and 
Santa Rosa, twigs often spring from the branch at the base of the 
spur instead of from the spur itself. If these twigs are not well 
thinned out, the tree soon becomes compact and the fruit spurs in 
that part of the tree are lost (see pi. 12, A). 
