Chapter VI. 



Fungi. Parasites of Plants. 



JS 



Effect of parasite on host. We have already seen that para- 

 sitism, in the broader sense, of a fungus on leaf-green plants 

 is always one of two kinds of partnership, equal or unequal, 

 and of the latter either the host or parasite may dominate. 

 Now, equal partnerships are rare, and those unequal associa- 

 tions with dominant hosts are also comparatively few, though 

 science is rapidly adding many new examples to the list already 

 known. The greatest number of partnerships are those in 

 which the parasite is the profit-making partner and the host 



Fig. 34. — Damping-off of seedlings, caused by a fungus (Pythium debaryanum) which 

 immediately kills the host plant — a low, though effective, type of parasitism. After 

 Atkinson, 



the loser. It has also been pointed out that dififerent fungi have 

 acquired dififerent degrees of efficiency in obtaining their prof- 

 its, and that highly specialized parasites can influence the host 

 to over-production of food stuffs for the benefit of the former. 



