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A TEXTBOOK OF BOTANY 



[Ch. X 



any visible sign, but 

 they are collected by 

 aid of pigs or dogs 

 which detect them by 

 their aromatic smell. 



Order 2, Pyrenomy- 

 cetes : the black 

 Fungi. These are par- 

 asites and saprophytes 

 of diverse forms and 

 manner of growth, but 

 characterized chiefly by 

 a compact, superficial 

 mycelium which has a 

 blackened aspect sug- 

 gestive of charring by 

 fire, — whence both 

 the Latin and English 

 names (the former 

 meaning "burnt 

 fungi"). The fructi- 

 fication is usually aper- 

 ithecium. Some 1 1 ,000 

 species are known, of 

 which many produce 

 destructive plant dis- 

 eases. 



One of the most 

 prominent of the group 

 is the Black Knot (Fig. 

 315), familiar in the 

 black swellings so 

 abundant on the branches of Cherry and Plum trees, to which 

 it does much damage. The parasitic mycelium ramifies at first 

 in the bark, but later breaks through to the surface, where, 



Fig. 315. — The Black Knot, Plowrightia 

 morbosa. 



Left, appearance of the Fungus on a branch 

 of Cherry, natural size. Right, above, the 

 superficial conidiophores, abstricting conidia ; 

 X 400. Next, cross section through twig and 

 sclerotium, and longitudinal section through 

 perithecia ; X 25. Below, an ascus, and 

 (right) , germinating ascospores ; X 300. (In 

 part from nature, and in part after Longyear.) 



