CHAP. Cl. ULMA'CEA. U’LMUS. 1389 
the death of certain elms in the public be 
walks in that city. Mr. Deck’s opinion h,- «sts 
was, that the trees were destroyed by ae 
the insects ; and Mr. Denson’s, that the AW 
trees were only attacked by the insects Nj 
after they had become injured or dis- SY 
eased. To prove this, Mr. Denson Wz 
selected in his own garden, in the spring ANY 
of 1828, a healthy young elm, about \ 
18 ft. high, and 1 ft. in diameter at the 4% 
surface of the ground. At about 30 in. a 
up the stem, that is, at 6, fig.1237, 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 ¢ d, 
and thence to have ed 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 a, 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 larve; 
while a 4 ¢ did not receive a single perforation, and now does not contain a 
single larva. This result satisfies my mind that the Scdlytus destractor 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 ae | 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 Muséum 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 
