Elm-destroyi7ig Scolytus. 365 



preceding year (1834) ; we may conclude, therefore, that, up to 

 the period when the falling of the young leaves took place, the 

 trees were healthy. To what, then, is the latter circumstance 

 attributable ? I have no hesitation in answering that the petioles 

 of the fallen leaves had been eaten into by the perfect scolyti Jbr 

 food. Although it is not recorded that such was the fact, the 

 observation which I have subsequently to produce clearly proves 

 the correctness of such an opinion. The loss of the leaves 

 would necessarily bring the trees into an unhealthy state, and 

 render them more especially acceptable to the female scolyti for 

 the reception of their eggs. The falling of the leaves occurred in 

 the spring, but the extreme dryness, under which it is maintained 

 that the trees suffered, did not take place until the middle and end 

 of the summer, by which time the trees were effectually attacked 

 by great numbers of the larvae. Can it be said, therefore, that 

 the death of the trees was owing to the extreme heat and drought, 

 when the presence of such vast numbers of insects in the spring 

 (indicated by so copious a fall of young leaves as to have at- 

 tracted the attention of the forest keepers) is so indisputably 

 proved ? No one will presume to deny that the presence of so 

 many hundreds of thousands of larvae boring through the sap- 

 vessels of a tree is not amply sufficient to cause its death ; and, 

 when we know that the elms in our parks infested to this extent 

 are killed, whilst those which are not infested still survive, I 

 cannot comprehend what sufficient reason there can be for not 

 regarding the scolytus as the chief cause of the injuries we sus- 

 tain. If, indeed, it could be shown that the elms decayed without 

 the scolyti being present, there would be some good ground for 

 laying the charge of the injury either to the heat of the weather, 

 or the long-continued drought, or the impurity of the atmosphere 

 acting upon the leaves in the neighbourhood of large cities, or the 

 prevention of a due supply of moisture to the roots of the trees 

 in our public promenades by compact coatings of gravel, all of 

 which have been at various times maintained to be the causes of 

 the mischief. So long, however, as the trees infested by scolyti 

 die, and those uninfested hy the larvcE of the scolyti survive, I 

 think there are ample grounds for maintaining the opinion that 

 the scolyti are our enemies in this respect. 



The following is an extract from my note-book : — 

 "In the month of July last, M. V. Audouin directed my at- 

 tention to a fine young oak tree (belonging, I believe, to the 

 species Quercus lusitanica) growing in the Jardin des Plantes, 

 which at that time appeared in a dying state, the leaves of all 

 the young shoots being either withered, or the shoots themselves 

 fallen to the ground. It had assumed this appearance about a 

 month ; and, on examination, it was discovered that it was owing 

 to the attacks of a small species of scolytus, which M. V. 

 Audouin considered to be Scolytus pygmae^us. This insect 



