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The Canadian Horticulturist. 



I 



different orders. Prof. Webster, in "Entomological News," for October, 1893, 

 records having bred nine distinct species from one lot of knots 

 collected in a single garden, and this collection did not include 

 the plum curculio, well known to breed in the knots, as well as 

 in the fruit. 



The black knot is a gall or woody growth, caused by the 

 attack of a parasitic fungus. In this gall when fully or partially 

 developed, many kinds of insects make their home and feed upon 

 its substance. Galls upon plants are caused either by parasitic 

 plants or insects. Gall insects are divided into gall makers and 

 inquilines, or guest flies. The former of these cause the gall, and 

 the latter only live upon its substance. Both of these classes of 

 insects are frequently infested by parasites, and in the case of the 

 black knot, which is a fungus, all insects bred from the knots 

 would be inquilines or parasites. 



In an excellent bulletin on this subject by Prof. B. D. Hal- 

 sted (New Jersey Ag. Col, No. 78), the life history of this 

 parasite is given at length and an appeal is made to fruit growers 

 to , induce them to make greater efforts to eradicate so perni- 

 cious a foe. 



Prof. Halsted says : In the first place, let the reader get 

 a clear understanding of the nature of the enemy that it is pro- 

 posed to conquer. There is no question whatever about the 

 black knot being caused by a low form of vegetable growth 

 called a fungus, that sends its minute threads through the sub- 

 stance of the twigs and branches. It is, therefore, necessary to gain 

 a knowledge of this fungus, and for this purpose the accompanying 

 engravings have been prepared. While it is generally assumed 

 that the appearance of the disease is familiar to most of our 

 readers, it has been thought well to give some illustrations. 

 [These illustrations have been kindly lent to us by Prof. Halsted 

 for this article.] 



The beginnings of a young knot are first seen in a manifest 

 swelling of the young twig, which is soon followed by a cracking 

 of the bark, and in the rifts thus formed the threads of the fun- 

 FiG. (M8. gus come to the surface and clothe it with a covering of olive 

 filaments bearing multitudes of spores. A young branch is shown in Fig. 648, 

 that exhibits the characteristic swelling of the initial knot and the cracks in the 

 bark in which the spores are borne. A highly-magnified portion of a rift in the 

 bark is shown in Fig. 649, in which *the superficial stalks and their spores are 

 seen. These spores are carried in all directions by the wind, and falling upon 

 the surface of young shoots, germinate, send their filaments through the bark 

 into the growing ring of soft tissue beneath and institute another knot. 



