104 



NUTRITIVE CONJUNCTIVE SYMBIOSIS 



soil a tuber-like body. Only the flowering shoot comes above the 

 surface of the soil. In some species the contact with the host is 

 only at a single point which may be on a small lateral root at some 

 distance from the main stem of the host. 



The Kafflesiacese is a tropical family of root parasites. In the 

 genus RafHesia the entire vegetative part of the plant grows within 

 the host, just as is the case with many parasitic fungi, so that the 

 plant ordinarily is seen only when it is in flower. Rafflesia Arnoldii, 

 one of these parasites, has the largest flowers that are known. They 

 are sometimes as much as a meter in diameter. 



Fig. 49. — Arceulhobium Douglasii (dwarf mistletoe). Staminate plants on Pseu- 

 dotsuga taxifolia. (Photograph by James R. Weu\) 



Among the most familiar partial parasites are the mistletoes; 

 Viscinn, the European mistletoe, Phoradcndron, the American 

 mistletoe, and Arceuihohium, the dwarf mistletoe (Figs. 48 and 49). 

 These plants contain chlorophyll and manufacture their own carbo- 

 hydrates but they are parasitic on the trunks and branches of trees 

 and obtain water and minerals from the host plants. 



The family Scrophulariacese contains representatives of all grada- 

 tions from complete independence to holoparasitism. Many of the 



