98 BIOLOGY 



the mycelium being essentially alike, although a single plant 

 may contain hundreds of these cells in its growing, branching 

 mycelium. 



Reproduction. The only noticeable differentiation of cells 

 that is seen in Penidllium occurs after the plant has grown 

 for a few days and is ready for multiplication. There may then 

 be seen arising from the mycelium minute branches that extend 

 vertically into the air instead of growing horizontally over the 

 surface of the object upon which the mold is nourishing itself. 

 These rise from the mycelium, simply as branches, and are 

 known as aerial hyphae (Gr. hyphe = web) ; Fig. 42 B and C. 

 The ends of these hyphae branch into a number of finger-like 

 processes, which extend vertically, parallel with each other, as 

 shown at C; after a time these branches divide by constriction 

 into rows of minute balls. These little spheres eventually break 

 off from the plant and then, blown by the wind, are scattered 

 far and wide. Each of them is capable, under proper conditions 

 of jnoisture and temperature, of developing into a new plant. 

 They are evidently spores, this particular kind of a spore 

 being named conidia (Gr. konis = dust). The conidia are 

 bluish in color and they cause the mold, which is at first white, 

 to assume a distinct blue tinge, giving to this plant its common 

 name of blue mold. They are extremely light and may be 

 blown for a long distance before settling to the ground. When- 

 ever they do settle upon any moist place they germinate; 

 each spore produces a new thread which in the course of a 

 few days becomes a new, branching mycelium and thus forms 

 a new mold. The conidia produced by a single plant are very 

 numerous and so light that they may be carried for a long time 

 in the air. Indeed, the air is at all times more or less filled 

 with them, in summer and winter alike; and it follows that 

 any moist material which will furnish them with food, like 

 bread, or pieces of lemon, or the surface of any fruit, if exposed 

 to the air for a short time, will be sown with these little spores, 

 and in a few days will begin to show signs of molding. So 



