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latter stores up. He also concludes that the swellings are produced solely 

 by the mechanical action of the tongue, and that they in themselves are the 

 cause of the trouble, by absorbing in tlieir development, the nourishment 

 needed for the vine, and by affecting, in rotting, the parts not touched by 

 Phylloxera: in other words, that the amount of nourishment appropriated 

 by the lice would never seriously affect the vine, were it not for the char- 

 acteristic and intrinsic swellings. I can not accept the last two conclusions. • 

 There is a strong a priori probability that the swellings are due to some- 

 thino- more than mere mechanical action — to some poisonous excretive 

 fluid, as in many gall-flies (Ci/nipidce) and saw-flies {Tenthredinidce) \ or to 

 some irritating and poisonous property of the proboscis, as in the spines 

 and hairs of many larvje. We may not be able to analyze it, but it is dif- 

 ficult to understand how, without some such poisonous property, the Phyl- 

 loxera leaf-gall is developed, while so many other plant-lice perform similar 

 mechanical acts to that performed by Phylloxera without causing abnormal 

 growths on the plants they infest. Bearing in mind also, the withering and 

 blasting effects which many plant-lice and bark-lice cause to plants which 

 never swell abnormally from tbeir punctures, it would seem obvious that 

 with the vine roots covered with Phylloxeras, most of them rapidly de- 

 veloping and multiplying, the direct loss of plant substance must be very 

 material — however great the indirect loss through the swellings may be. 

 There are any number of plant-lice no larger than our Phylloxera, and 

 which there is every reason to believe appropriate no more for the nourish- 

 ment of their bodies, which nevertheless affect most seriously the plants 

 they inhabit by direct sucking of the plant juices." 



Do not the anatomical researches of Targioni-Tozzetti and 

 Mark, in showing the possession, by Phylloxera and other 

 Aphididae, of such- conspicuous salivary glands, lend additional 

 weight to my view of the subject, and do they not give strong 

 presumptive evidence that there is introduced into the plant- 

 tissues, with the puncture of the proboscis, a secretion which 

 acts upon the plant in a peculiar manner, according to the spe- 

 cies ? In other words, have we not a right to assume an anal- 

 ogy between the puncture of the aphididan proboscis and the 

 cynipidan ovipositor ? On no other hypothesis can we explain, 

 with any degree of satisfaction, the production of a dozen or 

 more essentially different gall-growths (as by the different spe- 

 cies of Phylloxera affecting the hickory) on the same plant by 

 insects differing in no appreciable manner from each other, so 

 far as size and structure of proboscis are concei'ned. 



C. V. Riley. 

 Washington, D.G., 20 Feb., 1879. 



