74 STATE POMOLOGICAL SOCIETY. 



Lettek of Hon. Ltman Keed. 



QuiNCY Hall, 

 Boston, January 2G, 187G. 



Dear Sir: — I take pleasure in acknowledging the receipt of your valued 

 letter of the 24th inst. In answer, I have to say that I have never made fruit 

 trees a subject of special investigation. I have, from incidental observation, 

 however, some fads procured from microscopic research, which have satisfied 

 me that the black knot and the fungus so often found about the branches and 

 the fruit on plum and cherry trees, invariably results from the attack and rav- 

 ages of insects, many of which, in the larvai, are entirely microscopic — hence 

 the injurj- which they produce is so difficult to be accurately and definitely 

 traced. The microscope is too little chiployed by agriculturists and horticul- 

 turists. Those not accustomed to its use know nothing of the truly wonderful 

 developments which are continually working, in secret, in the various tissues 

 of vegetation, shrubbery and fruit trees. Nearly every vegetable, grain or 

 grass, as aleo shrubbery and trees, are inhabited by some kind of entomological 

 parasite. My investigations and micro-icopic researclies have been confined 

 almost exclusively to the potato, and to trace out the liabits, transformations 

 and general history of the insect. I will explain to you, however, what has 

 incidentally been observed about fruit. 



In 1839, I occupied a place in Baltimore (suburb of the city), Maryland. It 

 was an old estate, well stocked with fruit trees. Among them were choice 

 varieties of plums ; but the trees were young (8 or 10 years' growth), and bore 

 an abundance of beautiful fruit, and all sound. The bark of these trees was 

 smooth and free from moss. After a residence in Massachusetts for a number 

 of years, where I made the discovery of insects about the roots of potato vines, 

 I resided again in Baltimore and occupied the same place referred to above. 

 The luxuriant plum trees of 1839 had, in 20 years, become moss-grown, with 

 black knots and warts ; still they were filled profusely with blossoms each year, 

 and the early part of the season the fruit grew rapidly; but as the plums be- 

 gan to ripen they were uniformly covered with fungus (white mould). My 

 previous microscopic researches in Massachusetts, (Waltham), induced me to 

 examine those frees. My first attention was fastened to an unusual appear- 

 ance about all the branches, at the joints of each year's growth. 



Each joint was covered with a ring of small warts, 8 to 10 in number, encir- 

 cling every branch — the size about the head of a small tack. The warts about 

 the joints of previous years were tenantless, but the joint at the commence- 

 ment of the new wood or growth, where the plums were hanging, were firm 

 and tightly closed. By cutting open tliese warts, the center exhibited to the 

 natural vision a minute, white speck. Upon a microscopic examination of the 

 dissected wart, I found and counted distinctly from 20 to 40 living, microscopic 

 larva; insects in each half wart, as it lay under the focus of the instrument. 

 Thus was revealed to me an army of secret depredators. They were living 

 upon the sap, and their presence, from their attack or by emanation from their 

 bodies, conveyed a virus to the growing fruit; and thus the poison infused by 

 the insects, passed by exhalation to the surface of the plum, producing the 

 mould or fungus. These larva; remained in these warts through the season, 



