REPORT OF THE SOCIETY 87 



spores which ripen and become Hberated about May. A Httle later on, a 

 second crop of spores is produced. This mass darkens and the entire 

 surface becomes quite black and charred in appearance. These are the 

 winter spore cases. They become fully developed about mid-winter and 

 shed their contents at the end of the winter or early the next spring. 



The life history of the fungus is as follows: — When a spore becomes 

 liberated and finds a favourable germinating spot, it sends down a tube 

 through the epidermis of the plant into the cambium and bast areas, thence 

 to the cortex. Here the mycelium is abundantly produced and the cell 

 walls, tissues and vessels of the host are broken up in great disorder as 

 a consequence. The mycelium then finds its way to the surface through 

 small light green spots, tearing and breaking up the bark as it goes and ex- 

 posing the abnormal tissue of the knot beneath. From this covering arise 

 the summer spore-bearing bodies, in thick, compact, velvety masses. They 

 are upright, slightly curved at the tips and may further become branched 

 or bent as the brown spores are formed at or near the tips. After these 

 summer spores ripen they are blown away to other branches, where 

 they germinate, if conditions are favourable. This stage of the disease 

 lasts until about mid-summer when very small, black, pimple-like bodies 

 begin to appear among the green velvety masses of summer spore cases. 

 These are the winter spore cases and contain very large numbers of the 

 winter spores. The spores ripen towards the end of the winter or early 

 spring, when they are shed from their black cases and infect other branches 

 and twigs. 



The control of this disease is not a difficult one. Careful pruning and 

 burning of all knots before they reach maturity is considered the simplest 

 and most efficient means of dealing with the Black Knot. 



A good method of control is to spray the trees with Bordeaux Mixture 

 or lime sulphur towards the end of the winter and aga as the buds show 

 signs of swelling. Then follow this with two or three i.i' er sprays. Mr, 

 Gussow, Dominion Botanist, in his 1911 report, considers that spraying 

 for Black Knot is hardly a paying proposition. Cornell Exp Mation, N.Y. 

 State, on the other hand, reports that it is profitable and publishes a bulletin, 

 No. 81, as the result of experiments conducted there, to show a reduction 

 of Knots from 2,000 to 165. 



Mr. McCubbin, Plant Pathologist at St. Catharines, Ont.,in a bulletin, 

 No. 24, reports Bordeaux Mixture, various chemicals, tars, and paints, 

 all good controllers. 



In cases of bad infestation, the wisest and best method is to cut the trees 

 down and burn them. 



