THE BLA.CK-SPOT DISEASE OF CLOVER. 



42i 



In the earlier part of the season 

 small whitish or pale-brown spots 

 appear in the leaf, which contains the 

 mycelium of a fungus. This fruits 

 on the lower surface, producing num- 

 erous tufts of necklace-shaped threads, 

 each of which ends in a 2-celled, egg- 

 shaped conidia-spore. These tufts 

 of threads, which, like the spores, are 

 of a deep brown color, are packed so 

 closely together as to completely cover 

 the spots, though under a hand lens 

 j^^jji^y they can be distinguished as separate 



pauules. To the naked eye they appear dead-black. Later 

 in the season similar spots are occupied by small, coal-black 

 fruits that contain stylospores. Winter spores, produced in asci, 

 are not known. 



The conidial form of this fungus 

 ^1 (called Polytlirincium trifolii) is 

 especially common on white clover, 

 though both forms are at times found 

 abundantly on red clover and other 

 species. Kiihn suggests growing 

 grass with the clover as a means of 

 lessening its injury. (See Fig. 170.) 



Fia. 170. 



54 



Fig. :: 



