80 



FUXCtI AXD PUnTGICIDES 



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 liber of cotton wool. It is the 

 growth of these threads through the tissues of the berry 

 which causes the decay and shriveling, exterually mani- 

 fest as black rot. 



Microscopic Characters. — At points beneath 

 the cuticle the mycelium collects inro little knots, which 

 afterwards develop into the black pustules seen upon 



tiie surface. The.-e pus- 

 tules are globular riiick- 

 walled sacs or cuncepta- 

 cles, technically pijrnid\<u 

 which at maturity are filled 

 ^^^^^ with elliptical spores, 



Fia. 38. BIT OF SKIN SHOWING PUS- ^^^^^^'^ sfyJospores, The 

 TULEs. "\viTH ESCAPING COILED stvlo-porcs commouiV es- 

 MASSES OE SPOKES. MAGNiEiED. ^.^^^^^^ 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 : througli the pore in 

 the summit of four of them the coiled masses e)f siiores 

 are escaping.*' 



These stylospores are scattereel through tlie A-ine- 

 yard, and those which loelge upon green grapes "\vitii a 

 drop of moisture present^ germinate tjy seneling 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 ftmgus. They 

 are called by botanists the spermafia, the conicUa. and 

 the ascospores. The latter are produced in May and 

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



