PLATE 36 



Photographs enlarged from portions of a motion photomicrograph, showing the 

 method of cell wall penetration by Pythium hyphae. 



A. — Shows hypha growing toward the potato cell wall. 



B. — Shows hypha attached to wall and about to penetrate. 



C. — The tip has just broken through the wall. 



D. — The penetration is complete. Note the black line at the point where the 

 hypha penetrates the wall. This may be due to a rolling up of the potato cell wall 

 about the hypha or to a difference in refraction caused by compression of the wall. 



