PEACH YELLOWS. 291 



ly in trees which have begun to bear, I have found no dwarfing, and yet have 

 discovered aphides on the roots, but only in small numbers. 



On the young and tender roots they settle in colonies, heads together and 

 beaks thrust into the soft tissues, from which they abstract the juice. This 

 constant sucking renders the root extremities flabby, and death ensues, where- 

 upon the colony migrates to another root, or, what is more likely, is carried 

 there by the yellow ant {Lasius claviger, Rogers), which is a constant atten- 

 dant. This pumping of root juices, with the consequent destruction of thous- 

 ands of root extremities, acts somewhat like severe root pruning. If too 

 many roots are removed the tree dies; if not so many, it is dwarfed. 



The foliage of such trees is greatly dwarfed. It also presents miserable red- 

 dish or yellowish-green aspect, with more m less rolling and curling, and 

 purple-spotting of the edges of the leaf. This appearance is known as 

 ^'Frenching," and. is quite constant on young trees, although I have known 

 instances in which it did not occur. Ordinarily, from the appearance of the 

 parts of the tree above ground, one is very safe in diagnosing root aphides, 

 as I know from repeated trials. 



When I first began field work I was surprised and puzzled by occasional 

 reports of "dead spots" in orchards, i. e., places where peach trees will not 

 grow. Afterwards, I examined many such spots and satisfied myself that the 

 trouble is due to root aphides, at least in Maryland and Delaware. I have 

 seen spots of soil, not noticeably different from the rest of the orchard, on 

 which the second and even the third planting languished and finally died 

 with symptoms such as I have detailed. This languishing is frequently con- 

 founded with yellows, but it is entirely different. Sometimes by repeated 

 trials healthy trees have been grown in such places. 



I believe the aphides are retained in such spots or transported to other 

 localities by the yellow ant which I have found constantly associated with it, 

 and which appears to be the only species taking any interest in this aphis. I 

 have frequently found the eggs, larvas and pupaj of this ant in sandy soil 

 under peach trees ; and have seen the ants take the aphides very tenderly in 

 their jaws and remove them to places of safety. In one instance, while 

 digging in orchard No. 16, I placed a small root containing a colony of about 

 thirty aphides on the ground at some distance from the tree, intending to 

 put them into alcohol. Before I discovered what they were doing, yellow 

 ants had carried away all but four or five, and were still carrying. I saw one 

 ant come and go three times, each time taking away an aphis in its jaws, and 

 each time very tenderly. Undoubtedly this aphis is carried from root to root 

 and tree to tree by these yellow ants. 



What makes this subject interesting in connection with peach yellows is 

 the theory that that disease is due to the depradations of this insect. In view 

 of the ravages of Phylloxera in vineyards, it is certainly an attractive theory 

 and one to which I have given much thought. 



Some time after I began my field work, I found them in a number of 

 orchards on roots of trees suffering from yellows. At first I was much per- 

 plexed, thinking I might have overlooked their presence on many roots 

 previously examined. This discovery led me to make many exhaustive and 

 very tedious underground examinations, in some cases 50 to 75 cubic feet of 

 earth being turned over under a single tree, all the roots and rootlets therein 

 being examined very minutely, often with a triplet. These examinations 

 somewhat restored my confidence in previous work. In a number of orchards 



