292 STATE HORTICULTURAL SOCIETY. 



I found trees in various stages of yellows, on the roots of which the most 

 patient and prolonged search revealed no aphides. The yellow ants were also 

 absent from the soil. This, however, is not conclusive, for it is well known 

 that the Phylloxera generally abandons the roots of badly diseased vines for 

 healthy ones, and the same might be true of this aphis. Although the roots 

 gave no positive indication of the previous presence of these insects, I could 

 not deuy that they might at some time have been present and have deserted 

 these roots for those of other trees, which would in turn fall a prey to yel- 

 lows, to be in turn deserted. While this could not be denied, it nevertheless 

 seemed improbable, because on the roots of large trees I never in any instance 

 found them in numbers sufficient to do much injury. Only one experiment 

 looking toward the settlement of this point was undertaken. In 1887, in the 

 southwest part of orchard No. 14 of this report, the roots of twelve trees were 

 very systematically examined, an entire day being spent in the digging. "", Six 

 of these trees had become diseased by yellows in ]887, and six were entirely 

 healthy. I found aphides in small numbers on a few of the roots of 1, 3, 4,. 

 5, 6, 7, 9, 10, and 12. In the earth under the other trees (two diseased and 

 one healthy) I saw no yellow aots, and found no aphides on their roots. In 

 August, 1888, these trees were re-examined ; 4, 8, and 9 had become dis- 

 eased, while 5, 6, and 7 continued to be healthy: i. e , No. 8, on which no 

 aphides were found in August, 1887, had become diseased, and Nos. 5, 6, and 

 7, on which they were found, had not become diseased. So far as it gofes, 

 this result is opposed to the aphis theory. 



A much stronger objection is the well-established fact that trees whose 

 roots have been seriously infested with aphides often recover or linger on for 

 years, with none of the symptoms of yellows. Young trees the first or second 

 •year out from the nursery often suffer severely from this root aphis and after- 

 wards recover, making healthy orchards. I have seen a number of such 

 orchards. 



Another serious objection is that at Denton, Caroline county, Md., and at 

 Bridgeville, Sussex county, Del., this root aphis has been more or less de- 

 structive since 1870, at times very destructive, while so far as known no- 

 trouble from yellows has ever been experienced at either place, both locali- 

 ties now being free, or nearly free, from that disease. This insect has also 

 seriously injured trees at Seaford, Del., in the orchards of Colonel Martin, 

 without having caused yellows. Some of the trees recovered, others died. 



One point remains to be discussed — that is, whether under any circum- 

 stances the root aphis may give rise to symptoms resembling yellows. The 

 symptoms already detailed are the common ones. I have heard it asserted 

 that the aphis causes peaches to ripen prematurely, and the well-known fact 

 that such ripening mky be brought about by severe root- pruning lends some 

 countenance to the belief. My examinations, however, developed no proofs. 

 I have seen green, healthy peaches on trees badly infested by root aphides, 

 and when I have found this insect on the roots of tries bearing premature 

 peaches it has never been under such circumstances as to render it certain, or 

 even probable, that it was the real cause of the disease. The only point 

 about which I have any doubt is whether such growths as that shown in 

 Photo. VI can ever result from attacks of the aphis. This photograph was 

 made in autumn from a tree set in spring, and the top shown is the only 

 growth it made during the entire season. The roots were infested by this 

 aphis, and seemingly to an extent fully sufficient to cause the symptoms ob- 



