398 



LIFE ON THE EARTH 



FIGURE 129 



pendent plants, or fungi, such as the mushrooms (Figure 

 129) and toadstools. Mushrooms are widely used as a deli- 

 cacy and their growth is an important industry in some 

 sections. They are grown in soils very rich in humus and 

 generally in dark, cellarlike places. The 

 mushrooms that grow wild in the woods 

 are abundant in some localities but 

 should not be used for food unless most 

 carefully examined by some one who 

 is expert in determining the different 

 species. There are several species of 

 mushrooms which are exceedingly poison- 

 ous. For one of these there is no known antidote. The 

 general structure of these larger fungi can be seen by 

 examining a mushroom obtained from the market. 



The bacterium is a single-celled de- 

 pendent plant, probably the simplest 

 of all plants ; it can be seen only with 

 a high-power microscope. Bacteria 

 are rod-shaped, thread-shaped, screw- 

 shaped, or have various other forms 

 (Figure 130). The protoplasm in the 

 cell of bacteria has the power to as- 

 similate food and build more proto- 

 plasm. When the cell has grown 

 sufficiently, it divides into two cells. 



A healthy bacterium grows fast 

 enough to be ready to divide about 

 once an hour. If it divided once an hour and each division 

 continued to divide once an hour, in the course of twenty- 

 four hours there would be nearly seventeen million bacteria 

 produced. If this were kept up for some weeks, the mass 



' 





> ~" 



A^ 



FIGURE 130 



