54 FUXGI AXD FUNGICIDES 



that lodge upon the tender bark of young shoots send 

 out germinating tubes and start other knots. 



^'^As the season advances," says l)r. Halsted, '^the 

 young knots and the fresh growth of older ones lose 

 their olive, velvety appearance, turn a dark color, and 



develop a hard incrusta- 



/a ^^^. ti on on the surface. With- 



.^^/"qQ ^ (P ^^ ^^^^ substance oi this 



^^ ^i®*^ % black and brittle layer 



^ © I %^ many spherical pits are 



oQ ^^^Ic^.^ i p formed, and, as winter 



g«e 3^Q p^ '^^•3^ #^^^ K advances, minute sacs are 



^ W^'/*^ Q^ .^o'^*/?l'^"* produced upon the wall of 



00^ % ^^ the cavity, that toward 



J ^^ ^ spring bear each eight 



^ ^ oval bodies that are known 



FIG. 26. SPORES OF BROWN ROT. ^s sac sporcs. Thcsc 

 MAGNIFIED. cscapc from their long 



sacs and pass out through a pore at the top of the cav- 

 ity, and are then carried by the winds to the surface of 

 a young cherry or plum 

 twig, and thus begin 

 another knot, which, in 

 the course of time, pro- 

 duces a new crop of sum- 

 mer, and another of winter 

 spores, and thus the dis- 

 ease is preserved and 

 propagated." fig. 27. brown rot spores ger- 



Treatment.-Theonly ^"nating. magnified. 



successful treatment for a badly infested tree is to cut 

 and burn it, trunk, branch and all. All knots on trees 

 but little affected should be cut and hurned. Never 

 throw the removed knots on the ground, as spores are 

 developed off as well as on the tree. When young 

 knots appear on large limbs, or on limbs that one does 



