18 WOODPECKERS IX RELATION TO TREES. 
is no doubt thai cambium, bast, and sap arc depended upon by sap- 
suckers as staple diet. 
The results of sapsucker attacks on trees are so uniform and char- 
acteristic as to be distinguished easily from the work of other wood- 
peckers. Sapsucker holes are drilled clear through the bark and 
cambium and often into the wood. They vary in outline from cir- 
cular to squarish elliptical, in the latter case usually having the 
longer diameter across the limb or trunk. Generally they are ar- 
ranged in rings or partial rings around the trunk, but they often fall 
into vertical series. Deeply-cut holes arranged with such regularity 
are made only by sapsuckers. 
After the original pattern of holes is completed, the sapsuckers 
oft (>n continue their work, taking out the bark between holes until 
sometimes large areas are cleanly removed. This often occurs on 
small limbs or trunks, where long strips of bark up and down the 
tree are removed, leaving narrow strings between. This effect is also 
produced by continually enlarging single punctures by excavating at 
the upper end (PI. V, fig. 4), which is done to secure fresh inner bark 
and a constant supply of sap. Occasionally, after a tree has been 
checkered or grooved after the above-described systematic methods, 
it may be barked indiscriminately, leaving only ragged patches of 
bark. (PI. V, fig. 5.) Even in such cases, however, traces of the 
regularly arranged punctures are likely to remain, and there is no 
difficulty in recognizing the work as that of sapsuckers, for no other 
woodpecker makes anything like it on sound, living trees. 
All holes, grooves, or irregular openings made by sapsuckers 
penetrate at least to the outermost layer of sapwood or nongrowing 
part of the tree. Tliis results in the removal of the exterior rough 
bark, the delicate inner bark or bast, and the cambium. Since the 
elaborated sap (upon which the growth of trees depends) is conveyed 
and stored in these layers, it is evident that sapsuckers attack the 
trees in a vital part. Each ring of punctures severs at its particular 
level part of the sap-carrying vessels, another ring made above 
destroys others, and so the process continues until in extreme cases 
circulation of elaborated sap stops and the tree dies. When the 
injury to the vital tissues is not carried so far, only a limb here and 
there may die, or the tree may only have its vitality lowered for a 
few years. If the attacks cease, it may completely recover. 
EFFECTS OF SAPSUCKER WORK ON THE EXTERNAL APPEAR- 
ANCE OF TREES. 
Recovery, however, does not mean that the tree has escaped per- 
manent injury. Patches of cambium of varying size may be killed. 
Growth ceases at these points and the dead and discolored areas are 
