156 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



large quantity of suitable breeding-material may cause an increase 

 in the numbers of these insects that will jeopardise the healthy 

 trees. A particular form of injury inflicted by some of these 

 beetles is that of attacking and breeding in the crown and upper 

 branches of old trees whose vitality is not great. This attack, 

 which spreads down the branches till the main trunk is involved, 

 has been described on certain deciduous trees, and is of im- 

 portance as likely to be overlooked. 



Damage by storm, snowfall, frost, or by forest fires, or cater- 

 pillar-defoliation, together with careless forestry and the slovenly 

 accumulation of loppings, felled timber, and unbarked logs, serve 

 to foster the development of such insects till serious injury is 

 risked. The thin-barked Spruce suffers more than the Pine, and 

 it was the forests of this tree that were so terribly ravaged by 

 bark-beetles in the Harz Mountains during the last century. 



Except the Pine-beetle {Myelophilus i:)iiiiijerda), no bark- 

 beetles cause extensive damage in Great Britain ; still many 

 injurious kinds do occur which might cause trouble if the 

 circumstances which favour them be disregarded through over- 

 confidence in their supposed innocuousness. Every forest-tree 

 cannot possibly be in a perpetual state of robust health, and 

 there is one period when every tree is liable to insect-attacks — 

 after transplantation. 



That bark-beetles have been associated with the destruction 

 of trees over immense areas is undoubted ; and it lies with the 

 advocates of the theory that their presence is immaterial to show 

 what those forests would have died from in the absence of bark- 

 beetles, instead of invoking mysterious and unnamed " diseases." 

 The most serious attempt to prove another cause for the 

 destruction of the trees is that of Lindeman, who associated the 

 beetles with the presence of Agaricus melleiis. This, however, 

 appears to be definitely disproved. 



5. Not a few insects feed during some part of their lives on or 

 in the young shoots of Conifers, in the leader or the extremities 

 of the lateral branches. When the leader perishes the upward 

 growth is checked until one or more branches of the top whorl 

 twist round to supply its place. So lateral branches are de- 

 stroyed or have their growth stopped, and the tree becomes 

 altered in shape and appearance. Such mutilated Pines abound 

 in almost all woods in the South of England. 



