THE BLACK LOCUST TREE 215 



which the beetles escape from the burrows are not conspicuous. While 

 the bark remains unbroken the tree lives and usually continues annually 

 to produce its seed. The latter fact not only belies its hidden trouble, 

 but it is characteristic of the strong vitality of the tree. This vitality is 

 also exhibited by the roots which send up vigorous suckers, especially 

 after the borers have attacked the trunk. Again, the reciprocal rela- 

 tion of the tree and the insects which prey upon it, although it is never 

 wholly interrupted, is of more or less unstable equilibrium, sometimes 

 the tree, and sometimes the insects being ascendant. That is, it has 

 often happened in a given district that the tree became reduced in num- 

 bers to a few scattered and injured specimens, and its insect enemies 

 were correspondingly reduced in numbers because of the reduction of 

 their only means of subsistence. The native vigor of the tree then 

 gives it such advantage that it so thrives again that one naturally 

 hopes for its permanent immunity. But that improved condition of 

 the tree itself invites, and sooner or later receives, renewed attacks of 

 the insects, which lurk there or which come in from contiguous dis- 

 tricts. Such an oscillation of relative conditions occurs with the borer 

 especialbv,thus deceiving local observers as to the great average damaged 

 condition of the tree. The two insect species which have been men- 

 tioned as preying upon the leaves and tender twigs respectively have 

 their needs supplied by even the youngest, as well as the older, growth 

 of tree, but the borer requires a body of living wood of some inches in 

 diameter in which to produce burrows of sufficient extent for its needs. 

 Therefore this greatest of the insect enemies of the black locust tree is 

 held at bay until the tree has reached sufficient size for boring, during 

 which time the planter must await the issue. Meantime the young of 

 this tree generally grows as thriftily as the average of other trees, and 

 often it produces seed before it is large enough for the borers. It is not 

 strange that this early thrift of the tree should encourage disbelief of 

 impending evil for it, but the facts here mentioned are too well estab- 

 lished to admit of serious question. 



Exceptionally large and healthy specimens of the black locust tree 

 are sometimes found growing as a part of the native arboreal flora, 

 their, at least partial, immunity from insect injury doubtless being due 

 to local causes, some of which are obvious and some obscure. For ex- 

 ample, some of the best American specimens of the tree are found to 

 have grown in, or around, cattle-pens, barnyards or other farmstead 

 inclosures where domestic animals are gathered, the conditions of which 

 places are known to be favorable to the tree, and they are appar- 

 ently unfavorable to the insects. Again, the isolation of the tree 

 by planting its seeds in districts remote from those in which both 

 the tree and its insect enemies prevail, has resulted in the healthy 

 growth of the tree for many years ; but in most of such cases the trees 

 have been overtaken by the borers and destroyed or rendered valueless 



