192 The Elm and its Insect Enemies. 



The journals of more recent date abound with notices on the 

 same subject, and the discussion was reopened by a leading 

 article in the Times newspaper of the 30th January, 1862, 

 wherein the procede Robert was cautiously advocated as ' ' worth 

 a trial " in this country. 



That Scolytus destructor does bore through the bark of the 

 elm and feed on the alburnum is not to be disputed. But let it 

 be observed that the perforations are made in June and July, 

 when the sap is in full circulation, and any small wound in a 

 healthy tree heals over in the course of a few days. Let a 

 healthy tree be then selected and bored with an instrument, so 

 as to imitate as nearly as possible the action of the beetle. 

 The experiment may be made still more complete by inserting 

 in the borings some small shot or beads, in the same way as the 

 insects deposit their eggs. In the course of a week or less it 

 will be impossible to find those artificial perforations unless the 

 part of the tree where they were made was marked for the 

 purpose, and when the marks are examined, it will be found 

 that the sap has deposited new material sufficient to close 

 the perforations ; so that if, instead of shot or beads, real eggs 

 of Scolytus had been inserted, those eggs would be her- 

 metically sealed up, and nothing but a miracle would save the 

 larvee from perishing. I believe it can be proved to demon- 

 stration that the race of Scolytus destructor would be extermi- 

 nated in one season were the female beetles so misguided in 

 their instincts as to deposit their eggs in healthy elm-trees ; the 

 power of vegetation would annihilate the brood by investing 

 every cluster with vegetable tissue so dense as to cause their 

 suffocation, even if the eggs were hatched, and that event would 

 probably be as impossible as for the larvre to eat their way 

 either in or out. But elm- trees die, and are found on exami- 

 nation to be freely mined by these insects, yet they attest in 

 their death that the insects were not the cause of death, and 

 another experiment will explain it. Cut down a healthy elm, 

 and the next season the root will throw up a forest of suckers. 

 Ring a healthy tree, and unless it can form a new junction by 

 granular extension of the edges of the bark on both sides of 

 the ring, and on the upper edge especially, the same thing will 

 happen ; in fact, a healthy tree will refuse to be extinguished 

 unless assaulted above and below, and it is reasonable to con- 

 clude that if an army of Scolytus, Cossonus, and Cossus were to 

 commence their ravages in a tree previously in full vigour, the 

 diminished, vigour of the head would cause the roots to make 

 efforts at once to replace the head with strong shoots from the 

 roots. But when trees are found in a state of decay, and 

 apparently owing to the ravages of these insects, there is such 

 an absence of suckers and offshoots, that in that respect they 



