46 



PLANTS AND MAN 



cernible. One of the most distinctive features of the bacteria is 

 their characteristic shape, some being spherical, others rod- 

 shaped and still- others spiral. Whether saprophyte or parasite, 

 the bacterial cell absorbs its food from the surrounding environ- 

 ment; the protoplasm produces enzymes, similar in function to 

 those found in animal bodies, which are excreted into the en- 

 vironment. Acting upon the complex organic compounds of 

 plant or animal protoplasm, these enzymes break them down 

 into simple sugars or amino acids, which are absorbed into the 



cell and then used for respi- 

 ration, storage or growth. Be- 

 cause of this dependence upon 

 organic substances, bacteria 

 and other heterotrophic plants 

 are not found in environments 

 characterized only by inor- 

 ganic materials. This accounts 

 for their scarcity in clear lakes 

 or on bare earth surfaces, and 

 for their abundance in stag- 

 nant pools with decaying 

 bodies of plants or animals, 

 on food and in the tissues of 

 living organisms. Destructive 

 metabolism within the bac- 

 terial cell involves respiration 

 with the release of carbon 

 dioxide, water and vital 

 energy, though some species 

 have a special type of respiration with no need for oxygen. 

 Growth is by cell division, as in the desmid cell. The capsule or 

 sheath, already described, is an effective protective structure; 

 because of this, bacterial cells are often difficult to destroy. 



Molds are multicellular colorless plants roughly comparable 

 to some of the seaweeds. They are far smaller in size, most molds 

 forming a felt-like coating over organic materials. Some are 

 aquatic, and some terrestrial. Division of labor has resulted in 

 two parts to the mold's body. The general mass of colorless and 



BACILLUS 



(:DI^6(i/inMAT/c) 



BAC/LLUS 

 FORMING SPORES 



Fig. 22. — In contrast with the 

 desmid cell, the bacterial organism 

 has an exceedingly simple structure 

 with diffused nuclear material. 



