126 SOILS AND PLANT LIFE 



therefore manufacture their own food. (Section 66 and 

 Exercise 30.) 



(2) Those like the com smut, the cotton wilt, the wheat 

 and oats rust, the potato scab, the apple blight, the mush- 

 room and the toadstool. These contain no green coloring 

 matter, can not manufacture their own food and must 

 therefore draw their nourishment from living or dead plants 

 of other kinds. In so doing, they often cause either 

 diseases or decay. 



We are familiar with the destructive effect of plant 

 diseases and with the rotting of apples and potatoes. 

 We must not on this account, however, condemn all 

 plants of this second class. Many cause no injury, while 

 a multitude of them are beneficial and absolutely essential 

 to soil fertility and plant growth. The bodies of dead 

 plants must be broken down into simpler substances. 

 This necessary work is done by plants of this class, such 

 as molds and bacteria. (Section 5.) 



Place a piece of moist bread in any open, shallow dish 

 and set it aside for a few days. The whole surface will 

 become covered with common bread mold, a fuzzy growth 

 of minute plants, which develop when the spores floating 

 through the air fall and germinate upon the surface. 

 With a common hand lens, we can see dotted through this 

 growth the tiny round black bodies which bear the spores. 

 If it were not for the foul smelling gases, coming from the 

 decomposing proteins, which these plants set free, we 

 could leave the bread in the dish until the simple sub- 

 stances which molds invariably produce would alone re- 

 main. 



A striking illustration of the way in which the spores of 

 these minute disease-producing plants may exist is shown 

 in the common loose smut of oats. The smut spores are 

 carried with the seed oats from infested fields. When the 



