CHAP. CI. 



r/LMACEvK. LJ^'LMUS. 



38y 



the death of certain elms in the public , 



walks in that city. Mr. Deck's opinion f-ic'' 



was, that the trees were destroyed by ^ffiyV- 



the insects ; and Mr. Denson's, that the '^^^^V 



trees were only attacked by the insects >s^I/ 1^ 



after they had become injured or dis- -^^^T// 



eased. To prove this, Mr. Denson Ni^ 



selected in his own garden, in the spring 



of 1828, a healthy young elm, about ^^^;V-^, d 



18 ft. high, and 1 ft. in diameter at the 



surface of the ground. At about 30 in. ^^^^^^Y^ 



up the stem, that is, at b, fig.VZ'.M, he "^'^tiH^ 



says, " I cut out completely round the 



stem a band, or ring, of bark, about .:fr3'iU^.r^^ 



4 in. broad, expecting by this act to -4^!!^?^^^^^ 



intercept the passage of the sap to c d, ^^^^1^1^ 



and thence to have c d in a duly diseased ||j|ll|l ' ^^^s I^ 



and [)aralysed state, to be perforated by flPp' ^""^3^1^^ 



the scolytus in June or July ; while, by ■iff 5 --=jl-m i /- 

 retaining a alive, and in a growing state, Mmm^i ^^%K^/^ 

 I should be able to witness whether ^SbI'Ij ~^*^^^ / 

 the insect would attack the live part ^^o^ v ^[| \/^ 



also, or not. Quite contrary to my ex- ^^^fl ^^^^\W^^~ '' 



pectation, c d (the tree had been de- fflli:*^! ^^^^^'^t^^ 



prived of its head when I adopted it for lipi'l — ™-* 



my experiment) emitted side shoots, ''"li||'(| v(»V 



and grew as freely through the season ^f^^^^^^i^- 



of growth, both of 1828 and 1829, as a 



itself; evincing, indeed, no difference, either from «, or other elms stantling near 

 it, except that the leaves turned yellow somewhat earlier, and fell somewhat 

 sooner. Too impatient to wait longer, early in 1830, from c dl cut oW d, a 

 piece about 9 ft. long, and placed it near the remainder of the tree ; and, to my 

 great gratification, in June, d was visited by scolyti, perforated in many places, 

 and, from the eggs then deposited, now (Sept. 9. 1830) teems with larvae; 

 while a b c did not receive a single perforation, and now does not contain a 

 single larva. This result satisfies my mind that the Scolytus destructor is 

 altogether guiltless of causing the death of healthy growing trees." 



In this controversy, we are informed by William Spence, Esq., F.R.S.,who 

 has recently attended to this subject, that both parties, hke the knights who 

 quarrelled about the shield with one side of gold and the other of silver, are 

 both right and both wrong. It is quite true, as Mr. Denson maintains, that the 

 female scolyti never deposit their eggs in trees perfectly healthy ; but it is 

 equally true, that both they and the males pierce young and healthy trees 

 for the sake of eating the inner bark, which constitutes their food ; and that 

 the numerous holes which they thus cause, partly from the loss of sap which 

 exudes from them, and partly from the effect of the rain which lodges in them, 

 in a few years bring the trees in which they occur into that incipient state of 

 ill health in which the female selects them for laying her eggs, just as in trees 

 beginning to decay naturally ; and thus healthy trees are effectually destroyed 

 by the combined operations, first and last, of the scolyti of both sexes, though 

 not in consequence of the sole deposition of the eggs of the female. That 

 this explanation of the subject, so happily reconciling former apparently 

 contradictory facts, for which those who are interested in the preservation of 

 the elm are indebted to the distinguished naturalist, M. Audouin, professor 

 of entomology at the Museum d'Histoire Naturelle at Paris, who has 

 recently closely studied the habits of these insects, is correct, Mr. Spence, 

 to whom he communicated it this spring, informs us he has had numerous 

 opportunities of proving in the most satisfactory n)anner; having, both at 



