182 



BOTAh'Y. 



found which much resemble them and contain other sup- 

 posed reproductive bodies. 



332. No sexual organs have as yet been observed. Pos- 

 sibly they exist in the dense tissues of the knot, and fertil- 

 ization may occur in the spring or early summer, but they 



Fig. 104.— Structure of Black Knot. 1, filaments bearing conidia ; 3, sty- 

 lospores ; 3, a hollow papilla (perithecium) containing spore-sacs ; 4, spore- 

 sacs and spores, witli three slender filaments (paraphyses) ; 5, a spore ; 6, 

 spores germinating. All much magnified. 



have probably disappeared through the excessive para- 

 sitism of these plants. 



333. The parasitic filaments of each year's knot gener- 

 ally penetrate downward some centimetres into the unin- 

 jured bark, and remain dormant there until the following 

 spring, when they begin the growth which results in the 

 production of a new knot, as described above. 



334. To this order belongs the Ergot (a common para- 

 site upon heads of rye), and also many of the black growths 

 upon the bark and wood of trees. Many species produce 

 black spots upon living leaves, while many others occur 

 upon dead leaves and twigs. 



335. The Black Fungi include a large number of exceed- 



