A LEAF BLIGHT OF THE AMERICAN 

 MISTLETOE, PHORADENDRON 

 • FLAVESCENS (PURSH) NUTT. 



F. A. Wolf 

 (With Plate 32, Containing 3 Figures) 



The American mistletoe, which is known to be largely a water 

 parasite on various species of deciduous trees, is in turn the 

 host of several parasitic fungi. Attention was directed, during 

 the past year, to one of these fungi which causes a diseased 

 condition of the foliage. The material for the study and the 

 field notes on the general symptomology were furnished by 

 Professor Carl Hartmann, of Huntsville, Texas. A detailed 

 study as to the causal organism shows that the trouble is due to 

 an apparently undescribed species of Macro pho ma. 



Recently* a diseased condition of the twigs of the European 

 mistletoe, Viscum album, was described as occurring in Germany. 

 This was found to be due to Macro phoma Visci Aderh. That 

 this species of Macro pho ma is not identical with the one occur- 

 ring on the American mistletoe was clearly shown in the detailed 

 examination which was made. 



The disease manifests itself by chlorosis of a part or the whole 

 of the leaf, then the affected foliage becomes darker and is 

 finally dark-brown and dead. At this stage the leaves may fall, 

 so that in severe cases the entire plant may be defoliated, or, 

 as more frequently happens, only part of the leaves are killed. 

 Apparently, the injury to the mistletoe is only temporary, as it re- 

 news its activity with the seasonal growth of its host, and new 

 shoots and leaves are formed. 



The prominent pycnidia are quite uniformly scattered {pL ^2, 

 f. i) and are present on both leaf surfaces. They are formed 

 within the tissue of the leaf and at maturity rupture the epider- 

 mis and protrude by a central ostiole. They are globular or 

 somewhat flattened in shape, dark-brown in color, and vary in 



* Aderhold, Rud. Arb. Biol. Abt. Kaiserl. Gesundheitsamt 462-463. 1905. 



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