28 IOWA ACADEMY OF SCIENCE 



usually takes several years before the tree is killed. The fruiting bodies 

 of the fungus occur on the surface where they form numerous thin 

 brackets with a zonal marking on the upper surface and white under- 

 neath. 



KooT Rot of Oak, Etc. 



Hallimasch, Honey Agaric {Armillaria mellea Vahl.). The Honey 

 Agaric or Honey IMushroom has long been recognized as the cause of 

 root-rot 'disease of trees. Its parasitic nature was first described by 

 Hartig^° and later verified by many other investigators. During the 

 autumn of 1910 a large number of specimens were found in an oak 

 forest near Ames. They are found mostly, however, on the stumps of 

 young oaks cut off the previous winter; a few, however, in connection 

 with living trees. The general symptoms of the disease are a stunted 

 growth and gradual dying. In other cases the trees die suddenly, espe- 

 cially during dry weather. The diseased trees show a white mycelium 

 of a leathery consistency on the roots. There are also dark strands or 

 rhizomorphs, which are connected with the mycelium between the bark 

 and the wood. These rhizomorphs undoubtedly spread the fungus from 

 plant to plant. The fruiting bodies of the fungus appear in great 

 numbers in the fall and come from the rhizomorphs. Th^y are yel- 

 lowish brown, 2-4 inches across, with dark scales. The gills (lamellae) 

 are attached to the stem. There is also present an inner veil which 

 forms a distinct ring. The fruiting body is 3-8 inchs high. The spores 

 are elliptical, white and abundant. 



The Spot Disease op the Butternut and Black AValnut, or An- 



THRACNOSE. Gnomoiiia leptostyla (Fr.) Ces. and de Not. 



Marsonia Juglandis (Lib.) Sacc. 



For nearly twenty years the writer has observed this disease on the 

 black walnut and butternut. Though generally not regarded as a 

 serious disease by most observers, the writer is inclined to consider it 

 as much more serious than is usually supposed. It is not an uncommon 

 thing for the black walnut and butternut to lose their foliage during 

 the latter part of August because of the attacks of the Marsonia. Few 

 accounts have appeared in American literature. Selby^" states it may 

 do serious injury. I have also referred to its injurious nature in 



'"Wichtige Krankheiten d. Pflanzen. also Zersetzungerscheinungen, etc. 

 Galloway & Woods. Yearbook U. S. Dept. Agrl. lS96:2i9. 

 Tubeuf. Diseases of Plants. 455. 

 ^'Bull. Ohio Agrl. Exp. Sta. 214:452. 



