44 



THE POPULAR SCIENCE MONTHLY. 



cies growing on various substances, which have the general structure 

 of Fig. 6. 



We now come to the most common of all the members of the group 

 of moulds : the blue mould of cheese, bread, and almost every article 

 of food. In its diet, it does not confine itself to those things found in 

 a well-stocked pantry, but will flourish on old boots and other articles 

 of clothing when they are left for a few days in a warm, damp place. 

 Xo culture was made without its making its appearance, and often to 

 the exclusion of all other forms. It is quite small, never reaching but 

 a very short distance from the substance on which it grows, and under 

 favorable circumstances forms an even blue crust over the surface of 

 the nourishing material whether boots or bread. The structure of 

 this frequent and often unexpected and unwelcome visitor is given in 

 Fig. V. Two fully-developed fruit-stalks are seen at a and b, branching 



Fig. 7. Penicillium crustaceum. Fr. 



irregularly at the top, and bearing the naked spores in chains at the 

 ends of the filaments. At c is a young stalk before the spores have 

 formed from the threads, which is done by a constriction, a familiar 

 but perhaps rude illustration of which is seen in the making of the 

 links of sausage. As the spores fall away, new ones are formed below, 

 and so the process of producing these simplest of reproductive bodies 

 is indefinitely continued. At the base d are the threads which pene- 

 trate the nourishing substance, on some of which are formed, as the 

 result of sexual action, spherical bodies which inclose the more en- 

 during sexual spores. From this method of forming subterranean 

 fruit this little mould is a close relative to the truffle so highly prized 

 for food. 



