THE WOOLLY APHIS. 27 



inability to sell badly infested trees, and not from the death of the 

 trees themselves. 



The woolly-aphis sucking the juices, from the roots of the apple 

 tree causes an abnormal gro\vth of the attacked portion of the roots, 

 resulting in the formation of gall-like swellings or excresences. 



These swellings are usually irregular and knotty in appearance, and 

 sometimes attain considerable size, while that portion of the roots 

 between the excresences is frequently undeveloped. 



The woolly-aphis will be found in large numbers, and in clusters, 

 over the surface swellings, and especially between them in the 

 numerous crevices that the larger excresences contain. The roots thus 

 attacked, distorted and swollen, soon begin to decompose ; saprophytic 

 fungi and bacteria enter the dead and decaying portions and help to 

 hasten the work, and soon that portion of the root perishes. Sometimes 

 the root seems to be killed outright by the vast number of aphis sucking 

 the sap and causing the abnormal growth ; so that the attacked portion 

 perishes before decomposition has fairly set in. But in either case the 

 aphids perish, or leave the dead root and seek living roots upon which 

 they can feed ; and hence, when one examines a root that has been dead 

 for only a short time even, the aphis may not be found there, and this has 

 led many to attribute the death of the root to other causes, especially to 

 ' root-rot.' As the woolly-aphis attacks in immense numbers the main 

 roots at or near the trunk, and as these roots are usually eventually 

 killed and then rapidly decay, the tree loses its support and falls with 

 the first wind." 



There is a wide-spread opinion that the root form and that in the 

 branches are two distant species, but there seems little, if any, evidence 

 to support such views. With reference to this, Mr. Stedman carried 

 out the following experiment : 



" On the fourteenth of March, seedling and one-year-old apple 

 trees were planted in the root-cages. The plants w r ere first thoroughly 

 cleansed of all insect life, as eggs, etc., and the earth used was specially 

 prepared and free from insects and their eggs. On the sixteenth of 

 March, wingless, agamic female woolly-aphis, just obtained from the 

 roots of an infested apple tree, were placed on the roots of the 

 sound trees in four of these cages. These root-cages are kept 

 isolated in one room of the green-house, two of them in large 

 breeding cages made of glass and very fine wire gauze, so that no 

 insects could escape or others possibly enter. The apple trees soon put 

 forth leaves and grew well. The aphids multiplied rapidly and not only 

 formed colonies where introduced on the roots, but they soon spread in 

 small numbers over the greater portion of the roots, established colonies 

 near the trunk, and crawled up to trunk and on to the branches, where 

 they multiplied rapidly and established flourishing colonies. These 

 colonies can be seen on the branches as well as on the roots of the 



