214 



THE CANADIAN HORTICULTURIST. 



\ 



THE BLACK KNOT. 



As the leaves fall away from the 

 Plum and Cherry trees, conspicuous 

 excrescences are frequently seen upon 

 the branches, which, from their shape 

 and color, have appropriately received 

 the name of Black Knot. This is an 

 old enemy of the fruit garden, and its 

 ravages have been so severe in some 

 parts of the country, especially the 

 older sections, that the raising of Plums 

 has been given up. Though known as 

 a very destructive growth upon the 

 trees for a long time, it is but within 

 the last few years that its nature has 

 become known beyond a doubt, through 

 the careful and prolonged study of scien- 

 tific men. 



The history of the investigations into 

 the nature of the Black Knot would 

 make a volume of no small size, and of 

 interest in more ways than one. The 

 insect theory prevailed for a long time ; 

 and there seemed to be v^ery strong 

 indications that the Knot was similar 

 in origin to the galls of the Oak, Willow, 

 etc. The fact that the excrescences, 

 especially the old ones, contained living 

 insects, their eggs, and remains of the 

 dead, was taken as positive evidence 

 that the " house " they occupied was 

 built by the indwelling insects. The 

 Knot is now known to be of fungus 

 origin, and therefore is related to the 

 Peach curl. Potato rot, Wheat rust, 

 and a long list of other microscopic 

 plants too small to be seen, except by 

 their destructive effects, as they pi'ey 

 upon the higher forms of vegetation. 

 The fungus, or parasitic plant, was first 

 described in 1838, but it remained for 

 Dr. Farlow, of Harvard University, to 

 publish a full account of the minute 

 plant, and its methods of propagation 

 and growth. I can do no better than 

 to give the argument against the insect 

 theory, or for the fungus nature of the 

 Knot, as briefly presented by Dr. Far- 

 low : *' First, the Knots do not resem- 



ble the galls made by any known insects. 

 Secondly, although insects, or remains 

 of insects, are generally found in old 

 Knots, in most cases no insects at all are 

 found in them when young. Thirdly, 

 the insects that have been found by 

 entomologists in the Knots are not all 

 of one species, but of several different 

 species, which a»-e also found on trees 

 that are never affected by the Knot. 

 On the other hand, we never have the 

 Black Knot without the Sphceria mor- 

 bosa [the scientific name of the fungus], 

 and the mycelium of that fungus is 

 found in the slightly swollen stem, long 

 before anything that could be called a 

 Knot has made its appearance on the 

 branch ; and, furthermore, is not known 

 to occur anywhere except in connection 

 with the Knots." 



The Knots range in size from an inch 

 to a foot in length, usually growing 

 upon one side of the branch, causing it 

 to bend away from that side, or twist 

 irregularly. The parasite first makes 

 its appearance in the spring, when the 

 affected branch increases rapidly in 

 size, and becomes soft in texture. The 

 bark is soon ruptured in various places, 

 and the soft interior comes to the sur- 

 face, expands rapidly, and soon turns 

 green. Multitudes of minute spores 

 are formed on this exposed green sur- 

 face, which fall away and are carried 

 by the winds, etc., to other twigs, thus 

 propagating the disease. These spores 

 continue to be formed until late autumn, 

 when the surface of the Knot takes on 

 a dry and black surface ; in the mean- 

 time, insects may have taken possession 

 of the soft tissue within, and so eaten 

 and destroyed it that at the end of the 

 season only a thick, hard crust, or shell, 

 remains. Another kind of spore is 

 found in small pits and sacks of the 

 crust, and as they form late in autumn, 

 they are the winter spores of the.fungus, 

 and the form in which the pest is carried 

 through tlie winter. These spores ger- 



