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 (Orobanchacece) . 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 
