CHAP. CI. 



ULMA CEJE. tf'LMUS. 



1 389 



l^3< 



the death of certain elms in the public 

 walks in that city. Mr. Deck's opinion 

 was, that the trees were destroyed by 

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

 trees were only attacked by the insects 

 after they had become injured or dis- 

 eased. "To prove this, Mr. Denson 

 selected in his own garden, in the spring 

 of 1828, a healthy young elm, about 

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

 surface of the ground. At about 30 in. 

 up the stem, that is, at b, Jlg.\2'37, he 

 says, " 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, 

 and thence to have c d in a duly diseased 

 and paralysed state, to be perforated by 

 the scolytus in June or July ; while, by 

 retaining a alive, and in a growing state, 

 I should be able to witness whether 

 the insect would attack the live part 

 also, or not. Quite contrary to my ex- 

 pectation, c d (the tree had been de- 

 prived of its head when I adopted it for 

 my experiment) emitted side shoots, 

 and grew as freely through the season 

 of growth, both of 1828 and 1829, as a 



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

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

 sooner. Too impatient to wait longer, early in 1830, from c d I cut off 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, like 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 manner; having, both at 



