216 Plant Life and Evolution 



dependent to a greater or less degree upon other 

 organisms for their substance. It is among the 

 higher flowering plants that the most remarkable 

 parasites and saprophytes occur. The most extreme 

 parasites are found in certain tropical and sub- 

 tropical species, of which the extraordinary Raf- 

 flesia of Sumatra may be taken as a type. This 

 parasite passes the whole of its vegetative existence 

 within the tissues of its host, a species of wild vine, 

 and the vegetative structures of the parasite are so 

 reduced, that they more nearly resemble the myce- 

 lium of a fungus than the body of a normal flower- 

 ing plant, and the parasite feeds upon its host some- 

 what in the same way that the fungus does, the 

 tissues being in direct communication with the con- 

 ducting tissues of the host. At maturity enormous 

 flower buds are formed, which burst through the 

 outer tissues of the host, and the gigantic flower 

 expands and develops its seeds exposed to the air. 

 The extraordinary degradation of these endo-para- 

 sitic flowering plants makes it very difficult to ascer- 

 tain their relationships. Complete parasitism, but 

 less extreme, is met with in a good many more or 

 less familiar plants. The dodder is one of the 

 best-known forms, and is a genuine parasite upon 

 a variety of other plants, twining its leafless stems 

 about them, and sending suckers into the host 

 from which it derives all its nourishment. The 

 leaves are reduced to scales and only a slight trace 

 of chlorophyll can be detected. Many of these para- 



