1$2 Zoology, 



bitant has enclosed the mouth of the shell with a beautiful web, so that it 

 cannot sink, but floats on the surface ; and thus the precious charge 

 receives the vivifying powers of the sun, and is hatched into life. The 

 natural history of this little spider is extremely interesting; particularly the 

 mode in which it forms its web under the water. In this it lives, being 

 surrounded by air which shines through the water with a silvery lustre. 

 See Kirby and Spence, and some recent popular works on natural history. 



— G. M. Lynn Regis, Dec. 1. 1830. 



Scolytiis destructor not a Destroyer of healthy . Trees,. — Sir, Letter A. is 

 a reprint from the Cambridge Chronicle : letter B. is a reply I prepared to it, 

 but which the editor, wishing to give time to Mr. Deck's experimental 

 application of the oil of tar, declined to insert. Letter C, which I address 

 to you, includes my subsequent researches on the subject. I am. Sir, &g. 



— John Densony sen. * Waterbeach, near Cambridge , Sept. 9. 1830. 



[A.] 

 Sir, The sudden decay of some of the elm trees in front of Catherine 

 Hall having much excited the public attention, and given rise to a variety 

 of erroneous opinions respecting its cause, 1 am induced to offer a few 

 remarks upon this subject (the result of personal observation and experi- 

 ment), as it is one of deep interest to all who possess woodlands and orna- 

 mental plantations. It appears to be a prevailing opinion in the vicinity of 

 Cambridge, that when the roots of a tree penetrate the gault or blue clay, 

 which extends over a large portion of the county, and in geological posi- 

 tion lies immediately below the chalk, they cease to derive nourishment, 

 and soon perish ; but sufficient satisfactory evidence not having been 

 adduced upon this point, I give no credit to the hypothesis, having in 

 repeated instances found the real source of the evil to proceed from the 

 same cause as in the trees above alluded to, as well as in some which have 

 perished in the plantations of Madingley Park. Tiieir death has been 

 decidedly occasioned by the ravages of a small beetle, of the genus Scolytus, 

 and of the species emphatically termed destructor. This insect penetrates 

 the bark till it reaches the alburnum or soft wood. It is in this portion of 

 the tree, and the inner bark or liber contiguous to it, that the vital principle 

 more especially resides; and here the female insect works her way for 

 about two inches, in a direction parallel to the surface, and in her progress 

 deposits numerous eggs. About September these are hatched into the 

 grub or larva state, and from this period the work of destruction com- 

 mences. The young grubs eat their way into the alburnum and liber, at 

 right angles to the channel formed by the parent insect, and in parallel lines 

 to each other's progress. Thus very considerable patches are totally de- 

 prived of vitality ; and it will be readily understood that, when a tree has 

 numerous wounds of this nature in a part so important to its functions, 

 the circulation of its sap would be so impeded as to cause its immediate 

 decay. From September to March, by removing a portion of the bark, 

 the larvae may be found of the size and much resembling the nut maggot ; 

 and about the latter end of May the perfect insects begin to make their 

 appearance. These soon eat their way through the bark, and in June 

 and July may be observed busily employed in preparing to deposit a fresh 

 stock of eggs, for the propagation of a new brood of grubs, the harbingers 

 of destruction for the ensuing year. When a tree has perished, they no 

 longer lay their eggs in it, but proceed to those in its immediate vicinity 

 (a remarkable instance of which is exemplified in their ravages at Mading- 

 ley), which are destroyed with greater facility, as the increase of the species 



* Author of A Peasants Voice to Landowners, reviewed in the Gardener^ s 

 Jfa^azme for February, 1831. — Cond. - 



