80 



FUNGI AND FUNGICIDES 



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 concept a- 

 cles, technically pycni<lin, 

 which at maturity are filled 

 with elliptical spores, 



FIG. 38. BIT OF SKIN SHOWING PUS- kllOWI1 aS ^lOSpOTeS. The 



TITLES, WITH ESCAPING COILED stylospores commonly es- 



MASSES OF SPOKES. MAGNIFIED. ^ thrQUgh fln aper t Ure 



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, whjch 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 spermatia, the conidia, and 

 the ascospores. The latter are produced in May and 

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



