2 BULLETIN UNITED STATES GEOLOGICAL SUEVEY. [Tol.\. 



affecting" Uhmis emnpestrk.*- This autlior, by a series of ingenious ex- 

 periments, rightly came to tlie conclnsion that the insects hibernate on 

 the trunk ; but he failed to discover in what condition they so hiber- 

 nate. 



M. J. Lichtenstein of Montpellier, France, who has paid mucli atten- 

 tion to these insects, was led to the behef, announced in various publi- 

 cations t during the year 1877, that the European species inhabiting Elm 

 and Poplar migrated to the roots of grasses and there hibernated. He 

 was doubtless misled b^' the great general resemblance between aU the 

 species of this sub-family in the immature and apterous stages. In a 

 letter dated December 25, 1877, I informed him that I had discovered 

 that the sexed individuals of our Ehn species inhabited the bark, to 

 which the female consigned her single winter agg, and that his theory 

 was altogether inconsistent with this fact and Avith what Derbes had 

 discovered of Pemphigus cornicularius affecting Firs.f With this clue 

 my friend has done good service the past season, by correctly tracing the 

 life-liistory of several species, and showing that tTiere are no such nii- 

 grations as he assumed, from the trees in question. Indeed, nothing but 

 the most thorough and absolute proof can establish the fact of any such 

 migration. Species of the same genus often so closely resemble eacli 

 other that they are more readily distinguished by their mode of life, or 

 by the galls they produce, than by structural or describable differences ; 

 and this holds particularly true of the immature or apterous stages. 

 This fact, taken in connection with what is here recorded and what is 

 already known of the habits of the sub-family, renders it extremely im- 

 probable that any of the species subsist at one time on one plant and 

 habitually change, by migTation, to another of a totally different nature. 

 Stranger things happen in nature 5 but until M. Lichtenstein experi- 

 mentally i:)roves tbe accuracy of his conclusions, I must reject his theory. 



Led by previous investigations into the habits of the Grape Phylloxera, 

 I discovered, in 1875, that some of our Elm-feeding species of Fem- 

 pMgincB produce wingless and mouthless males and females, and that 

 the female lays but one solitary impregnated egg, just as in the case of 

 Phylloxera. Continuing my investigations, especially during' the x)resent 

 summer (1878), I have been able to trace the life-history of those species 

 producing galls on our own Elms, and to show that they all agree in this 

 res])ect, and that the impregnated egg i^roduced by the female is con- 

 signed to the sheltered i^ortions of the ti-unk of the tree, and there liibei- 

 nates — the issue therefrom being the stem-mother,§ which founds the 

 gall-inhabiting colony the ensuing spring. Thus the question as to Avhat 

 becomes of the winged insects after they leave the galls is no longer an 



* DieLebensgescliiclite cler aiif Ulmns campestris Yorkommeiideu Apliiden-Axten. 



t Stettinex Eiit. Zeit. 1877, p. 489, &c. 



t Ann. cl. Sc. Nat. Paris, October, 1871. 



(^I adopt this term as a literal translation of the German " Stamm-mntter," and as 

 meaning the ancestress or progenitor of all succeeding generations until the impreg- 

 nated egg is produced and anotlier cycle commences. 



II 



