140 



THE CANADIAN HORTICULTURIST. 



Fig. 1780. Rhytisma acerinum (Maple Leaf 

 Blotch) showing the sclerotium spots, (a) on a 

 maple leaf. These sclerotia become wrinkled and 

 contain the apothecia with the asci and spores. 

 (Original). 



the winter, spores are produced in cavities 

 ■called asci, and in the spring- they become 

 mature and are liberated. In this way the 

 infection is carried to trees in the neig-hbor- 

 hood. 



The only practicable method of preventing 

 the spread of this fungus is to gather up and 

 burn the leaves before the spores are set 

 free in the spring-. 



(b) Pine Leaf-Cast {Lophodermiiim pinas- 

 tri). (Fig. 1 78 1.) Sometimes the leaves of 

 young, seedling pines fall prematurely, and, 

 if the leaves are examined, small, oval, black 

 spots may be seen. These are the masses 

 of asci, each containing eight spores, which 

 rupture only after long-continued wet 

 weather. In some of the islands of the 

 islands of the Muskoka lakes large areas of 

 young pine trees were completely defoliated 

 during the summer of 1899 by this fungus. 



No remedial treatment can be suggested 



for this disease, especially after the myce 

 Hum has gained an entrance to the inner 

 tissues. 



Summary. — Shade-trees are liable to at- 

 tacks from many quarters. Not only are 

 insect enemies plentiful, but fungous enemies 

 are even more abundant, and await the first 

 favorable opportunity to make the attack. 

 These opportunities come quite frequently 

 during the life of an ordinary shade-tree. 

 They come when outside conditions are 

 unfavorable to the healthy working of the 

 organs of the tree, when, for example, the 

 food supply is inadequate, the drainage poor, 

 or the water supply extreme. The tree be- 

 comes weakened, and in its weakened state 

 cannot ward oflF the host of invaders. 

 Wounds, brought on by storms of wind or 

 hail, when portions of the bark are bruised, 

 or branches torn off, form very suitable 

 places for the entrance of both fungi and in- 

 sects. In ever)^ case ths old adage, "a 

 stitch in time saves nine," holds true, and 

 frequently a little labor at the outbreak will 

 not only save a great amount of labor later 

 on, but also, perhaps, the life of the tree. 



The chief insect and fungous enemies of 

 shade trees have been discussed as fullv as 



Fig. 1781. Lophodermium pinastri (Pine Leaf 

 Cast, (i) leaves with the fungus. Within the 

 apothecia are the club-shaped asci which contain 

 the spores. (After Massee). 



