Zoology. 



155 



to life, they may be surrounded with the means of sustenance. The 

 perforations made by the pregnant Scolytus in effecting her ingress are 

 performed, as I believe, a short time previous to the death of the part per- 

 forated ; and because we no not seek the cause of death until that effect has 

 resulted, and in doing so find the Scolytus already in possession of the 

 part, we have too hastily stigmatised this insect as the cause of the death 

 and disease we witness. The Scolytus, in its very office and instincts, is 

 the concomitant of death and disease, but ever as a consequence, never as 

 a cause. 



While, however, I so zealously contend that the Scolytus never perfo- 

 rates a healthy living tree, I have the pleasure fully to agree with you that 

 it will never perforate an absolutely dead one. I take the Scolytus to be 

 the first agent in the process of transmutation. By the time its larvae 

 escape in a winged state from the part into which they were introduced in 

 the egg state, that part is wholly dead, and is never again perforated by 

 the Scolytus. Then succeed other tribes of insects to expedite the process 

 of decomposition or transmutation; and, after a series of species have 

 performed this office, the latter of these become themselves the food of *S'co- 

 lopendrae and other carnivorous insects. 



Let us, then, discard our apprehensions, nor longer impugn the Scolytus, 

 hitherto mistakenly called destructor, as the lawless destroyer of sylvan 

 magnificence, but, devising for it some more suitable epithet, behold here- 

 after its joyous revellings with sympathetic pleasure, or at least with indif- 

 ference. Thanking you for inducing me, by your letter, to express these 

 opinions, I am, Sir, yours, &c. — John DensoUy sen. Waterbeachy near Cam- 

 bridge, Jan,, 1828. 



[C] 



Sir, Pursuantly to writing letter B, I had recourse to experiment to 

 confirm or disprove the opinions there advanced. I selected, the same 



spring, in my own garden, a healthy 

 29 \rJllii^ young elm, about 18 ft. high and 1 ft. 



diameter at the surface of the ground. 

 At about 30 in. up the stem, that is, at 

 b {fig. 29.), I cut out completely round 

 the stem a band or ring of bark, about 

 4 in. broad, expecting by this act to 

 intercept the passage of the sap to c d, 



— d and thence to have c dm o. duly dis- 

 eased and paralysed state, to be per- 

 forated by the Scolytus in June or July; 

 while, by retaining a alive, and in a 

 growing state, I should be able to wit- 



— ness whether the insect would attack 

 the live part also or not. Quite con- 

 trary to my expectation, c d (the tree 

 had been deprived of its head when I 

 adopted it for my experiment) emitted 

 side shoots, and grew as freely through 

 the seasons of growth, both of 1828 

 and 1829; as« itself, evincing indeed on 

 difference either from a or other elms 

 standing near, except that the leaves 

 turned yellow somewhat earlier, and 

 fell somewhat sooner. Too impatient 

 to wait longer, early in 1830 from cd 

 I cut off d, a piece about 9 ft. long, 



and placed it near the remainder of the tree, and, to my great gratification. 



