136 



THE CANADIAN HORTICULTURIS7, 



Fig. 1774. Nectria ditissima (Apple-tree Can- 

 ker); (i) a branch recently attacked, the disease 

 entered at the axil of the small branch, a peri- 

 thecia ; (2) a branch diseased for some time, show- 

 ing the rugged, raised margin about the wound ; 

 (6) conidia spores; (7) germinating conidium- 

 spore ; (8) ascus containing spores— the asci are 

 contained in the perithecia. (After Massee.) 



(b) Cankers [Nectria and others). — The 

 cankers are not nearly such conspicuous ob- 

 jects as the shelf-fung^i. Some of the cank- 

 ers have dark colored fruiting^ forms, while 

 others have brig-ht red forms. Nearly every 

 kind of forest and shade tree is liable to in- 

 festation b)^ these fung-i, and the infested 

 trees are sources of rapid spread of the dis- 

 ease to the other trees of the park. 



The most common cankers are the Apple 

 Tree Canker, Spruce Canker, Larch Canker 

 and the Coral Spot Canker. ( i ) The Apple 

 Tree Canker [Nectria ditissima) is \ery fre- 

 quently found on the common forest an the 

 common forest and shade trees. Gaining" 

 an entrance through a wound, the mycelium 

 attacks the bark, which it destroys in a 

 characteristic manner. As the bark cracks 

 concentrically, the area of diseased portion 

 gradually enlarges, so that sometimes the 

 trunk is completely g'irdled. Usually the 

 diseased area is surrounded by a thick, ir- 

 regular margin, which is also quite charac- 



teristic. In late fall whitish cushions of 

 mycelium come to the surface, and produce 

 minute spores, while in spring bright red 

 cavities appear, containing the asci and 

 spores.. Fig. 1774). 



(2.) The, Spruce Canker, [Nectria cncurbi- 

 tula), is chiefly found on the spruce. The 

 fungus gains an entrance through a wound, 

 and attacks the tissues of the cortex and to 

 some extent the wood. When the bark 

 becomes moist the mycelium may come 

 to the surface and produce minute spores, 

 and later in the season red perithe- 

 cia are formed, and spores are liberated 

 from asci. 



(3.) The Coral Spot Canker, [Nectria Cin- 

 naharina), is often seen on maples, horse- 

 chestnuts, and red currants. This fung"us 

 is most commonly found on dead twigs and 

 branches, where the brig-ht coral-like warts 

 are frequently very conspicuous. Like the 

 spruce-canker the spores gferminate on beings 

 broug-ht to a wound, and the mycelium makes 

 its way into the tissues beneath. The coral 

 warts are not observed until the death of the 

 twig. 



(4.) The Larch Canker, [Peziza ivillkoni- 

 niii). (Fig^. 1775). In low-lying regions the 

 larch is frequently attacked by this fung-us, 

 which has found an entrance throug^h some 

 wound. The presence of resin on the dis- 

 eased twig-s, oozing from cracks in the bark, 

 and yellow, wilted leaves reveal the progress 

 of the disease. The spores are formed in 

 asci sunken in the infested spots. Year af- 

 ter year the canker spot enlarges, and soon 

 girdles the tree. The fung^us may be readily 

 recognized by the saucer-shaped fruiting- 

 area ; the internal part of the saucer being 

 orange-red, and the outside white and 

 downy. 



Remedies. — Since all these cankers are 

 wound parasites, it is necessary to keep a 

 strict watch on all our shade trees for 

 wounds. Whenever they are found they 

 should be dressed with a solution of green 



