480 CLOVER PEBONOSPORA. SEEDLING ROT. 



13. The clover peronospora, (Peronospora trifoliorum, 

 DeBary). A dirty white or purple-brown mold, often completely 

 Governing the lower surface of the leaves of clover, alfalfa, 

 none-such, etc. (See Fig. 175.) 



The life history of this species is quite 

 similar to that of the last, though they differ 

 greatly in appearance. The leaves that it 

 occurs on are paler than the others, and the 

 threads that escape through their stomata and 

 bear conidia are so numerous and bushy as to 

 form a dense coating on their under side. 

 PIG. 175. Oospores are produced in smaller numbers 



than in the last species, and, as they are thin-walled 

 and nearly colorless, they are only to be found after careful 

 microscopical examination. Another species of the same genus 

 (P. vicial, Berk.) is found on the leaves of vetches and of the 

 pea. 



14. The seedling rot, (Pythium debaryanum, Hesse). Caus- 

 ing young plants of clover, millet, corn, and many other species 

 to rot close to the ground. 



Several species of Pythium attack living plants. The present 

 species is said to be widely distributed in garden soil in Europe 

 and causes serious trouble by attacking seedling plants. It has 

 not been observed in America as yet, but can be recognized, if 

 found, by its effects on the plants, which quickly decay near the 

 ground. They contain a delicate, colorless mycelium that fruits 

 on the surface of the decaying parts, when these are kept damp, 

 producing conidia, swarm-spores, and oospores. 



Fairy-Ring Fungi. Bright green circles, several feet in 

 diameter, closely surrounded by a narrow strip of dead or dying 

 grass, are frequently seen in lawns or pastures, and are commonly 

 called " fairy-rings." They are caused by several species of 



