Minnesota Plant Diseases. 



"3 



Black molds (Mucorinece in part). These fungi are exceed- 

 ingly common plants found on starchy materials and hence 

 often called'bread molds. y\lthough they have descended from 

 water-inhabiting plants they have retained almost no trace of 

 an aquatic habit, with the exception of the requirement of a 

 moist atmosphere for growth. That is to say, there is no 

 formation of swimming spores ; for all of the spores, except 

 the resting spores, are distributed by the wind, though aided in 

 some cases by a special explosive apparatus. The spores, as in 

 other algal fungi, are of two kinds, viz. : the egg spores and 

 those produced without breeding. The former are formed by 

 a different method from that of the false mildew where an egg 

 and a dififerently shaped male thread branch are found. In the 

 black molds both breeding organs are alike in size and shape 

 and are indistinguishable, just as is the case in the pond scums 

 among the algae. The egg spore is a resting spore and is 

 provided with a large, thick, resistant, usually black-colored 

 coat. However, the most common form is that of the non- 

 sexually produced spore. These are 

 produced in tiny, black, spore-cases, 

 which appear like small, black points in 

 the mass of mold threads. Each case 

 contains a great number of spores which 

 escape by the breaking of the spore-case 

 wall and are blown about in the wind. 

 In some molds, which are particularly 

 abundant on horse dung, there is a swell- 

 ing in the thread just below the spore 

 case and this swelling acts as a syringe 

 bulb under pressure. When the spores 

 are ripe the whole spore case contents 

 are blown ofif at once and thrown a half- 

 foot or more .into the air. 



The black molds are of very great im- 

 portance on account of the damage which they cause to food 

 stuffs, particularly the starchy foods. Bread, cake and pastry, 

 when kept moist, will almost surely develop mold, because mold 

 spores are to be found in the air of almost any region and at 

 almost any time of the year. The black molds are all typically 



Fig. 46.— a black mold. The 

 black spore-cases are seen 

 on the ends of the fungus 

 threads. Highly magnified. 

 After Zopf. 



