480 MacDouGAL: INDUCED AND OCCASIONAL PARASITISM 
Explanation of plates 22-25 
PLATE 22. Opuntia in the angle of branch and stem of sahuaro. Drawn from 
a photograph. 
PLATE 23. Detail of roots of Opuntia parasitic on sahuaro. (See PLATE 22.) 
Drawn from a photogr. 
PLATE 24 Sbunlixe on Acacia. Drawn from a photograph made in 1909 by 
Dr. W. A. Cannon 
PLATE 25. Opuntia on Acacia in 1911. Photograph by the author. 
