Minnesota Plant Diseases. 



305 



and as they mature, change to yellowish, then brown, and finally 

 to a dark brown or black. The capsule is provided with thread- 

 like appendages, which are dark brown in co 1 or and tin- 

 branched, and are interwoven with the threads of the mycelium. 

 The mycelium sometimes forms brown spots on the leaves, 

 and if present in quantity, may very seriously interfere with the 

 nutrition of the leaf of the host plant and thereby occasion con- 

 siderable damage. Each capsule contains a number of egg- 

 shaped sacs, each of which contains about eight spores. The 

 spores are capable of growth, after a rest period, when placed 

 under proper conditions, e. g., out of doors in spring. When 

 germinating, a tube is sent out, which penetrates the epidermis 

 of the host. By a further growth and branching of this tube 

 the mvcelium is established. 



FIG. 153. "Black mold" of clover (Phyllachora trifolii), on leaves of white clover. Original. 



By the use of flowers of sulphur the spread and growth 

 of the disease can be prevented to some extent. Infected 

 plants should, however, be destroyed every year to get rid of the 

 sac-capsules. The disease is not often abundant enough to be 

 very troublesome. 



"Black mold" of clover [Phyllachora trifolii (P.) Fckl.]. 

 This is a very common fungus in Minnesota growing abundantly 

 on white and also on red clover. The summer stage is conspic- 

 uous, forming blackish spots on the leaves. The summer spores 



