410 MINNESOTA STATE HORTICULTURAL SOCIETY. 



There can be but few persons interested in horticulture, or even in 

 a general way in plants, who have not seen to their dismay or to 

 their astonishment that this disease is becoming- more and more 

 cominon, and that but few wild plum and cherrj^ trees can be found 

 ^vhich are not more or less disfigured by it. In the course of my 

 numerous trips, both in Minnesota and elsewhere, I have inade it a 

 point to question people possessing such trees about the origin of 

 the black knots, and have almost invariably received the reply that 

 it was a diseased condition of the sap, or that it had been caused by 

 an insect or by some other mysterious being. Some tried to prove 

 their case by cutting open the more recentlj^ infested twigs, and as 

 a general rule succeeded in uncovering some insects, and, presto — 

 cause and effect were proven be3^ond any doubt whatever. Quite a 

 number of insects utilize the succulent swelling first produced by 

 the disease and revel in its interior, sometimes to such an extent 

 that after leaving the twig there is little else left of the original 

 swelling than a loose and more or less twisted laj^er of bark. Among- 

 other insects the genuine plum curculio infests such swellings, and 

 the}' were bred from thein as early as 1818 bj^ Peck. 



But, notwithstanding all such evidences, the swelling is produced 

 bj' a fungus, recognized and described in 1831 by de Schweinitz. 

 More recently the whole matter has been settled beyond any doubt 

 or dispute by the careful researches of Dr. Farlow, who followed all 

 the metamorphoses undergone by the fungus in its host; he discov- 

 ered also the various spores of the fungus. It is strictly of amer- 

 ican origin and has not yet been introduced into Europe, like so 

 many others. All kinds of wild plums and cherries are affected, but 

 cultivated varieties do not escape, though the fungus seems to 

 attack certain varieties of plums by preference. Notwithstanding 

 the claims of originators of disease-proof varieties, their claims are 

 of no value when tested over a more extended region. 



The first indication of the disease can be noticed in the autumn as 

 a slight swelling of the branch near an old knot (Fig. 1, a), some- 

 times even some distance away from it. In the former case it is 

 probably caused by an extension of the vegetative mycelium in the 

 old knot; in the latter, it is a new infection by spores. When we cut 

 through such a young knot we can observe that the bark, and 

 chiefly the inner bark (Phloem), has become swollen, and in it may 

 be seen the bundles of intertwining threads of the fungus. During 

 the following spring these knots or swellings enlarge more and 

 more until the epidermis ruptures and a dark, greenish-brown 

 mass of tissue protrudes, evidently caused by an abnormal growth 

 induced by the fungus (Fig. 1, b). This mass is quite firm and suc- 

 culent, with an irregular and somewhat cracked surface, quite in- 

 viting to many species of insects. Late in May, we can observe upon 

 the surface of this mass very numerous erect threads (Fig. 1, c), 

 which give it a darkbrown velvety appearance. Upon these threads 

 the roundish summer-spores of the fungus are produced, which are 

 of a brownish color. Later in the season both threads and spores 

 disappear, the knot is no longer velvety, but becomes black, hard 

 and dry— in fact, is dead. Its surface is now divided into small 



