The Canadian Horticulturist. 



27 



As the season advances the young knots and the fresh growth of older 

 ones lose their olive, velvety appearance, turn a dark color, and develop a hard 

 incrustation upon the surface. Within the substance of this black and brittle 

 layer many spherical pits are formed, as shown in Fig. 650, and as winter 

 advances, minute sacs are produced upon the wall of the cavity, that toward 

 spring bear each eight oval bodies that are known as sac spores. These escape 

 from their long sacs and pass out through a pore at the top of the cavity, 

 and are then ready to be carried by the winds to the surface of a young cherrX 

 or plum twig, and thus begin another knot, which, in the course of time, pro- 

 duces a new crop of summer and another of winter spores, and thus the disease 

 is preserved and propagated. In Fig. 651 is shown two of the sacs with the 



Fig. 649. 



eight spores in eacli. A free spore is also shown in the process of germination. 

 It is a fact that cannot be too emphatically stated here that the ascospores above 

 mentioned are matured during the winter months, and that they will continue to 

 ripen when the knots have been removed from the tree and left undestroyed 

 upon the ground. 



There are other forms of spores besides the two already pointed out, but 

 their presence or absence does not change in the least the treatment that should 

 be given to diseased trees, and therefore may be omitted from special mention 

 The fact of their existence only strengthens the previous conviction that in the 

 black knot we have a fungus perennial in its character and wonderfully provided 

 with methods of spore formation for the rapid spreading of the malady at all 

 seasons of the year. 



