338 



STRUCTURE AND LIFE HISTORIES 



cases all stages are found from true parasitism of the fungus 

 on the root, through a mutually beneficial relationship, 

 to a parasitism of the root-cells on the fungus. Among 

 common trees having endotrophic mycorrhizas, may be 



FIG. 246. Cancer-root (Conopholis americana) , of the Broom-rape 

 family (Orobanchaceos) . The ovaries are developing into capsules. The 

 plant derives its name from the scaly cone. (Photo by Elsie M. 

 Kittredge.) 



mentioned the black maple, horse-chestnut, and black 

 walnut, and most of the heath family (Ericaceae), such 

 as trailing arbutus, huckleberry, wintergreen, heather, 

 laurel, and rhododendron. This is probably the chief 



