Insects Injurious to the Elm. 29 



this cause, pared off portions of the bark in longitudinal strips, 

 thus removing at once both the food and the protection of a 

 great portion of the insect enemies. This measure was, how- 

 ever ineffectual, and M. Robert next proceeded to strip off the 

 whole of the bark. This was considered by many a rash pro- 

 ceeding; but the event seems to prove that M. Robert was 

 right, for entire colonies of insects were thus destroyed, and 

 the bark, contrary to general expectation, is stated to have 

 been perfectly reproduced. M. Robert, having apparently 

 proved .the efficacy of his method in cases where trees were 

 attacked with scolytus, was called upon to apply his mode of 

 cure to diseased trees in many parts of the French provinces, 

 and also in Belgium; receiving various testimonial honours 

 from many learned and scientific associations. 



The severe method pursued by M, Robert may appear at 

 a first glance extremely rash, especially on taking into conside- 

 ration that the system of ringing only — that is, taking off a 

 narrow strip of bark all round the trunk — is a method used for 

 killing trees in forest clearings. Yet, we shall see, allowing his 

 results to be indisputable, that M. Robert's process may be 

 founded on sound botanical physiology. But let us first find the 

 insect enemies of the elm, and having acquired a just idea of 

 the exact nature of their ravages, consider whether the process 

 6f M. Robert be likely to prove efficacious for their destruction. 

 Among the most fatal of the tiny enemies of the elm, and 

 others of our largest forest trees, is the Cossonus linearis, a 

 terrible foe, for fresh specimens of which I am indebted to Mr. 

 E. A. Smith of the British Museum. The figure at page 30 will 

 convey a good idea of the insect in its perfect state. It is, 

 however, in its larva state that its devastations' are committed. 

 The larva is, as may be conceived from the size of the perfect 

 insect, very minute, and is a soft smooth grub totally devoid 

 of legs, but it is furnished with considerable muscular power, 

 and with powerful mandibles, with which it at the same time 

 takes its food and perforates its miniature tunnel. This tiny 

 creature does not only feed between the bark and the solid wood, 

 either on the delicate fiber or inner bark, or on the alburnum, that 

 is to say,- the last formed layer of wood, still in a soft state, but 

 eats its way right into the heart of the tree through the sound, 

 hard wood ; and for these deeply internal ravages M. Robert's 

 system offers no remedy. A colony of these creatures works 

 upon the doomed tree, till it becomes perforated in all direc- 

 tions, and through every part of its vital tissues. The symptoms 

 of disease soon show themselves ; it loses the power to put 

 forth its leaves ; and, deprived of the result of their important 

 functions, rapidly perishes. 



Another enemy which, as being exceedingly numerous, is per- 



