232 TEXTBOOK OF PLANT PHYSIOLOGY 



food products. Closely related to saprophytes are the parasites, 

 which feed on living organisms by robbing the nutritive substance 

 created by them. 



The principal differences between the nutrition of saprophytes 

 and autotrophic plants are really not so great. All the non-green 

 parts of a plant lead essentially a sort of saprophytic life, receiving 

 nutritive substances from the green parts. In fact, the proto- 

 plasm of the green cells themselves receives its main nutritive sub- 

 stance, the carbohydrates, in a prepared form from the green 

 plastids. 



Animals, likewise, feed on prepared organic compounds. A 

 very important difference is to be noted, however, between plant 

 saprophytes and animals. Though they do not have the ability to 

 synthesize carbohydrates from carbon dioxide and water, sapro- 

 phytic plants have to a full extent the characteristic capacity of 

 plants to synthesize protein substances from ammonia and carbo- 

 hydrates, while some of them can even reduce nitrates. Animals, 

 on the other hand, are entirely incapable of effecting such syn- 

 thesis. 



There are very few saprophytes among the higher plants, most 

 of them belonging to the orchids {Neottia, bird's-nest orchid). 

 The cause of this apparently lies in the fact that the roots of higher 

 plants have almost entirely lost the ability to absorb organic 

 substances. All attempts to grow higher plants artificially in 

 sterile solutions of organic substances have resulted in very weak 

 growth; and when kept in darkness such cultures have failed 

 completely. 



Lower plants, which absorb solutions not through roots, but by 

 their whole surface, are much more adapted to a saprophytic mode 

 of life. Many green algae (Ulva, Cladophora), but especially those 

 of the blue-green group, usually supplant their photosynthetic 

 activity by absorbing organic substances from without. They, 

 therefore, may be called facultative saprophytes. The large group 

 of the fungi consists entirely of saprophytes and parasites. 



Saprophytic microorganisms may be divided into two physio- 

 logical groups: Those of the first group are able to use almost all 

 forms of organic substances and can live on practically any dis- 

 integrating organic matter. Such are the numerous molds and 

 many bacteria. They play an extremely important role in nature. 

 By destroying the dead bodies of plants and animals, and by chang- 



