102 



NUTRITIVE CONJUNCTIVE SYMBIOSIS 



or partial parasites, obtain proteins from their hosts or manufacture 

 them themselves. It is not likely that they are all alike in this 

 respect. 



Plants that obtain their food from dead organic matter are called 

 saprophytes. These, of course, are not symbiotic, but there are many 

 fungi and bacteria that can live equally well as parasites or as sapro- 



FiG. 47.—Daedalea confragosa, a facultative parasite on willow 



phytes. Such organisms are called facultative parasites. ]Many of 

 the bracket fungi, such as Polyporus sulphureus, are of this nature. 

 (Fig. 47.) Such a plant gets into a living tree through a wound and 

 may live as a parasite in the tree for many years, but after the tree 

 is dead the fungus continues to grow as a saprophyte in the dead 

 wood. Fungi of the genus Cordyceps, likewise, cause diseases of 

 certain kinds of insects. They grow as parasites in the living insects 



