Orchid Diseases 297 



blanc,* who found it on orchids in greenhouses in 

 France. It is not known whether this rust is of any 

 importance in the United States, The only danger 

 consists in its being imported from abroad with im- 

 ported plants. The causal organism produces only 

 teleutospores. It feeds on its host by means of 

 haustoria sent into the interior of the cells (fig. 59, 

 d, 1-9.). 



Rust of Orchids 



Caused by Uredo behnickiana Henn. 



Symptoms. This rust does not produce any strik- 

 ing symptoms. Hence it may readily be overlooked. 

 AflFected leaves are covered with minute, reddish- 

 colored sori. When mature, the epidermal covering 

 of these sori breaks away and liberates a reddish 

 powder which is made up of thousands of the spores 

 of the fungus. This rust is found on living leaves 

 of Oncidium dasystelis and was described by Hen- 

 nings t as a serious disease of orchids imported to 

 Germany from Brazil. It is not known whether this 

 disease is present in this country. Its introduction 

 should therefore be guarded against. Uredo be- 

 hnickiana differs from U. onicidii Henn, in that the 

 latter causes rounded thickened red-brown spots on 

 Oncidium lavecanum. 



* Griffon, M. M., and Maublanc, Bui. Soc. Mycol. de France 25: 



13S-139. 1909- 

 t Hennings, P., Hedwigia 44: 169, 1904. 



