250 Science of Plant Life 



host. The yellow dodder, which lacks chlorophyll altogether, 

 is a common parasite related to the morning-glory. It 

 twines about green plants and sends small roots into them 

 to obtain its food. Some parasites may take all their food 

 from the host plant, as does the dodder ; others, like the 

 mistletoe, which contain some chlorophyll, may secure only 

 a part of their nourishment from the host. 



The bacteria and fungi form a great group of simple plants 

 which resemble the algae in structure, but which differ from 

 the algae in having' no chlorophyll. They must, therefore, 

 live as saprophytes or parasites. Either they grow on or in 

 living plants or animals and draw their food directly from them, 

 or they feed on organic matter. 



The bacteria. The best known and the most discussed of 

 all the simple plants are the bacteria. They are so intimately 

 related to human welfare that most persons, even though they 

 have never seen bacteria, know something about them. Bac- 

 teria constitute a group of one-celled plants, at once the 

 smallest in size, the simplest in structure, and the most 

 abundant of all plants. They live in immense numbers in 

 the water and in the upper layers of the soil, and they are 

 blown about in dust in the air. Some are too small to be seen 

 except with the highest powers of the microscope. Others 

 may be seen with an ordinary laboratory microscope. They 

 make up for the small size of the individual by their rapid 

 multiplication, and by the formation of colonies containing 

 countless numbers of individuals. Bacteria are responsible 

 for many of the diseases of men, animals, and plants, and 

 bacteria affect our lives in almost countless other ways. All 

 our modern methods of sanitation, quarantine, surgery, water 

 supply and sewage disposal, and much of our personal 



