APPLE-ROOT BLIGHT ITS GENERIC NAME. 7 



History, under the name of Eriosoma Pyri, All those Plant lice 

 Which were formerly included in Dr. Leach's genus Eriosoma, 

 which have all the veins of the wings simple, and those in the 

 disk of the hind pair two in number, now form the genus Pem- 

 phigus of Hartig (Germar's Zeitsch. vol. iii, p. 366), to which 

 genus it is therefore necessary to refer this insect.* Several of 

 the other species of this genus, as well as the present one, are 

 known to infest the roots of plants. I entertain scarcely a doubt 

 that this is the same species which Mr. Walker soon afterwards 

 described, from specimens obtained in Nova Scotia, under the 

 name of Pemphigu Jlimricanus ; though the length which he as- 

 signs to it (four lines) is rather greater than any individuals I 

 have met with. 



To our nurserymen it obviously belongs, to fully elucidate the 

 history of this species, ^ind the disease which it occasions, as they 

 enjoy opportunities lor observing it such as belong to no other 

 profession. The knots, or excrescences, occur both upon the 

 large roots of the Apple tree and their more slender, fibrous, 

 and capillary branches. In the single instance in which they 



* Mr. Westwood, In his Arcana Entomologia, vol. ii. p. S3, observes that the name Bryso- 

 •crypta (Byrsocrypta) of Haliday must be retained for Hartigs genus Pemphigus. And on 

 the next page we are told: " The generic name of Eriosoma (Leach) must take place of 

 that of Pemphigus, and be restricted to such species as differ from Aphis bursarius." There 

 is a contradiction here, which I can only account for by supposing the distinguished author, 

 who is so accurate a nomenclator, has inadvertently placed the name Pemphigus in the lat- 

 ter quotation, where he intended to insert Schizoncura. The first division of the old Lin- 

 nsean genus Aphis appears to have been made in 1819, when Sainouelle (in his Entomologist's 

 Companion, p. 232) published the genus Eriosoma from Dr. Leach's MSS., with the "E, 

 Mali, the Aphis lanigcra of authors," or the well-known Apple tree blight, as its type. 

 Samouelle's little work, truly a " Ui-eful Companion'' in its day, probably was not circulated 

 upon the Continent, and entomologists there seem to have been uninformed of its contents. 

 Several synonyms, in consequence, have unfortunately been introduced into the science. Five 

 years afterwards, Blot (in the Memoirs of the Linnasan Society of Calvados, vol. i. p. 114) 

 named the same insect Myzoxylus Mali, which name has been extensively circulated by 

 French writers. Still more recently, Hartig (in Germar's Zeitschrift, vol. iii. p. 367) has 

 proposed the name Schizoneura for this same genus; whilst Macquart has bestowed the name 

 Eriosoma upon a genus of flies, in the Order Biptcra. Mr. Westwood is clearly right in re- 

 taining Dr. Leach's name for the genus having Aphis lanigera as its type. 



With regard to the statement first made above, I would observe, Mr. Haliday first proposed 

 the genus llyrsocrypta, if I mistake not, in the Annals of Nat. Hist, for the year 1839, page 

 189, placing under this genus the Aphis Ulmi of Geoffroy, and a new species which he names 

 pallida. We henee regard the Ulmi and not the bursarius as the type of Mr. Haliday's 

 genus. Consequently the name Byrsocnpta must be retail, d for the genus which has Ulmi 

 for its typo, namely, the Tctrancura of Hartig; whilst his crius Pemphigus, with bursarius 

 as its type, is entitled to stand. I therefore give our Am' ican species under this name. 



