80 FU^s'GI AXD PUJS'GICIDES 



threads growing into and between the cells. These 

 threads which form the vegetating portion of the fun- 

 gus, technically mycelium, are in diameter only about 

 one-sixth that of a single fiber of cotton wool. It is the 

 growth of these threads through the tissues of the berry 

 which causes the decay and shriveling, externally mani- 

 fest as black rot. 



Microscopic Characters. — At points beneath 

 the cuticle the mycelium collects into little knots, which 

 afterwards develop into the black pustules seen upon 



the surface. These pus- 

 tules are globular thick- 

 walled sacs or concepta- 

 cles, technically pycnidia^ 

 which at maturity are filled 

 with elliptical spores, 



FIG. 38. 13IT OF SKIN SHOWING PUS- ^Hown as stylospores. The 



TULEs, WITH EscAPixG COILED stylosporcs commouly es- 



MASSES OF SPORES. MAGNIFIED. ^^^^^ through au apcrturc 



or pore in the summit of the pycnidium in the form of 

 threads; these threads are masses of spores glued to- 

 gether by some adherent substance. Fig. 38 represents 

 a small bit of the cuticle or skin of the grape, with the 

 pustules considerably magnified ; through the pore in 

 the summit of four of them the coiled masses of spores 

 are escaping." 



These stylospores are scattered through the vine- 

 yard, and those which lodge upon green grapes with a 

 drop of moisture present, germinate by sending out a 

 little tube, which penetrates the skin and starts the dis- 

 ease anew. 



Besides these stylospores, there are three other 

 kinds of spores produced by the black rot fungus. They 

 are called by botanists the ^permatia, the conidia, and 

 the ascospores. The latter are produced in May and 

 June, by the mycelium in the berries destroyed the pre- 



