98 



FUNGOID DISEASES 



Symptoms. — Where seedlings are too thick and 

 too moist, they turn yellow in patches ; and, due to 

 a weakened place in the stem, at the soil level, fall 

 over ; the attack spreading with amazing rapidity. 



Cause. — Indirectly the cause is too thick seeding 

 and too much moisture ; directly the fungus Pythium 

 de Baryanum is the culprit. Its branched non- 

 septate hyphae grow within the plant and draw 



Fig. 28. — Pythium de Baryanum: (i) Portion of mycelium bearing 

 conidia (C) at the ends of the branches ; (2) Sporangium with zoo- 

 spores enclosed (Z), a zoospore with a cilium or hair ; (3) Antheridium 

 and Oogonium ; after uniting a resting spore, called an oospore, is 

 formed. (After De Bary.) 



nourishment from the contents of the cells; result- 

 ing in the weakening of the part and consequent 

 falling over. Later the hyphse grow on the out- 

 side and may reach short distances to healthy 

 plants. 



Preventive Measures. — 



1. Do not sow too thickly. 



2. Do not shade seedlings too much or keep them 

 too moist. 



