The Black-rot of the Gil\pe, and its Control. 



211 



Pycnidia. 



Spores.., 







Germinated 

 @E-^ Spores 



The mycelium serves the treble purpose to the fungus of root, stem 

 and leaf. It alone develops a receptacle in which reproductive bodies 

 are produced, while the root, stem and leaf of the stalk of corn all con- 

 tribute to the production of an ear (seed). The fruiting bodies of the 

 fungus that contain the summer spores (Fig. i8o) are formed of very- 

 short interwoven branches of the mycelium which become thick-walled 

 and black, and are ^ 



known as pycnidia. 

 There is a small cir- 

 cular opening at the 

 top. The pycnidia 

 form a more or less 

 concentric ring on the 

 spot and there are 

 from 5 to 30 or more 

 of them on a single 

 spot, visible to the 

 naked eye as very 

 small pimples. The 



interior of each pyc- t- o 7^ ■ • ■ , , • , 



/-^ riG. 180 — Diagrammatic section tlirough a single pyc- 



nidium IS lined with a nidimn, showing how the snminer-sporcs are produced 

 laver of delicate club- '^^^^ ^"^^ ^^^^ germ-inate, {Greatly magnified.) 



shaped bodies. These are specialized mycelial threads, and the summer- 

 spores or pycnospores are formed on their tips. Summer-spores 

 are formed in this way until the pycnidia become filled with 

 them. 



Summer-spores. 



These spores are surrounded by a gelatinous substance. When a 

 drop of water is placed on a ripe pycnidium, this gelatinous substance 

 swells and the pycnospores are forced out through the hole in the top 

 in a fine white thread-like stream. (Fig. 180). The pycnospores germinate 

 in water in 18 to 24 hours, grow, form a new mycelium and produce 

 exactly the same effect as the winter-spores. They also have the par- 

 ticular advantage of being on the leaves or stems and later on the berries 

 from which the wind may carry them for considerable distance to other 

 vines. 



