April 26, 1895.] 



SCIENCE. 



459 



fore the larva hatches. One must, there- 

 fore, in reading Straton's Introduction, bear 

 in mind tliat he is treating solely oftheCy- 

 nipida^ Adler himself recognizes the fact, 

 so far as the Tenfhredinkhe are concerned, 

 from observations on Xemahis vaUignerii, 

 which produces a gall on Salix amigdalina ; 

 but in sweepingly denying it for the gall- 

 gnats (p. 100), on the score that they have 

 no piercing apparatus, he makes one of those 

 generalizations which the facts do not jus- 

 tify, as most of the gall-making species have 

 a very effective and specialized piercing ovi- 

 positor. This is, of coui-se, not homologic- 

 ally comparable to that of the Hymenop- 

 tera, but is no more exceptional than is the 

 wonderful piercing apparatus of Pronuba 

 among Lepidoptera, being, like this last, a 

 modificiition of the tubular tip of the abdo- 

 men and of the chitinous rods connected 

 therewith. 



Adler shows very conclusivelj^ that, in 

 spite of the great variation in form, size, 

 appearance and manner of formation, or 

 whether they grow from bud, blossom, leaf, 

 bark or root, galls spring invariably from 

 the zone of formative cells or the cambium 

 ring, just as indeed does the whole life of 

 the plant. These cells are the theatre of 

 actual metabolism. They are not differen- 

 tiated into stable tissue, but await a period 

 of developmental activity and possess the 

 very conditions essential to gall formation. 

 This explains the fact that Cyuipid galls 

 formed from punctures in the leaf almost 

 always begin on the under surface of the 

 leaf, since the cells of the upper surface 

 have become stable and do not respond to 

 any irritation applied to them ; while when 

 the eggs are laid in a dormant bud contain- 

 ing rudimentarj- leaves consisting of un- 

 modified cells, both surfaces may take part 

 in gall formation, the resulting gall, in sudi 

 case, growing through the leaf substance. 

 Again, when the egg is laid in the cambium 

 ring of the bark, there is a sharp zonal con- 



ti'ast in tlie resulting gall between the soft 

 and sappy parenchymatous cells and a 

 harder central zone of wood parenchj'ma 

 corresponding to the bast and to the wood 

 parenchyma, the softer parts of the gall 

 projecting from the bark while its woody 

 base penetrates into the woody tissue. 



From the above facts we come to under- 

 stand why from winter buds, /. e., where 

 eggs are laid during winter in a bud that is 

 dormant, only bud galls are produced, while 

 from buds pierced in spring, when meta- 

 bolism has begun, we get leaf-galls. More- 

 over, it has been proved by Adler, and ex- 

 plains the many failures in the eflbrts to 

 obtain gall growths by confining gall-flies 

 upon the plants, that if the parent fly fails 

 to reach the formative zone of cambium 

 cells the larva on hatching perishes without 

 forming a gall. Another interesting fact 

 which tlie writer has observed is that where 

 but one bud-gall is usually produced several 

 eggs are nevertheless inserted in the bud by 

 the parent, a prodigality not uncommon in 

 insects under similar circumstances, and 

 which has some profound significances 

 which we cannot discuss in this connection. 



On the question as to w'hat determines 

 the ultimate growth of each particular gall 

 so characteristic of its species Adler ven- 

 tures no theory or explanation; but all the 

 facts would indicate that it depends on the 

 specific quality of the larval secretion, each 

 having its distinct form of morbid poison 

 working in the same pathologic way as the 

 virus of the various eruptive diseases of 

 man. Bacteriology may, in fact, yet come 

 to our aid in this connection, as it has in 

 the study of the pathologic manifestations 

 of higher animals. 



The process of oviposition in the Cynipid.e 

 is a verj' elaborate one and has been much 

 written about. Adler gives a most full and 

 elaborate description of the mechanism of 

 the ovipositor, and particularly of the ven- 

 tral plates and bundles of muscles by which 



