566 DISEASES OF CULTIVATED PLANTS 



(Fckl.). The fungus forms a white mycelium on the surface 

 of the soil, which attacks the plants at the collar and destroys 

 the root. Numerous minute sclerotia are formed on the 

 dead parts, and the soil becomes infected. Under the 

 circumstances, fresh soil should be substituted, and the 

 infected soil spread over grass land as the only place where 

 it can do no further harm. 



Celery heart rot. Celery often suffers from a root rot 

 which causes the heart of the plant to become soft and 

 pulpy; finally the plant droops and dies. Sderotinia sckroti- 

 orum (Mass.) is the cause of injury; the conidial or Botrytis 

 stage of the fungus appears first on the diseased parts as a 

 grey mould, and is followed by the formation of numerous 

 small black sclerotia on the dead portions of the plant. If 

 these are allowed to remain on the land, future crops, with 

 the exception of cereals, are endangered. 



Details as to the method of treatment of this parasite have 

 been given earlier in this book. 



Onion bulb rot. Quite recently a crop of white Portugal 

 onions were destroyed by a wet rot, which caused the bulbs 

 to deliquesce and give off a most offensive odour. On 

 investigation it was found that Sderotinia sclerotiorum (Mass.) 

 was the cause of injury. On cutting open the bulbs, 

 numerous black sclerotia were found located between the 

 scales, which were also observed to be teeming with the 

 mycelium of the fungus. 



Monkey-nut leaf rust. The leaves of Arachis hypogea are 

 frequently attacked by Uredo arachidis (Lagerh.), which forms 

 scattered or crowded, minute sori on the under surface of the 

 leaf. 



Uredospores subglobose or ovoid, brown, minutely echinu- 

 late, 25-35 /* diam. 



As to whether there is any genetic connection between this 

 uredo and Uromyces arachidis (P. Henn.), parasitic on the 

 same host, is not known. 



U. arachidis. Sori on both surfaces of leaf; teleutospores 

 subglobose, elliptic or ovoid, clear brown, epispore thin, 

 almost smooth, or minutely verrucose, 22-28x20-26 ^ ; 

 pedicel fragile, hyaline, short. 



Celery leaf spot. This disease, caused by Phyllosticta apii 



