DETAILED ACCOUNT OF SPECIFIC DISEASES OF PLANTS 



truncate at the base and measure 28 to 30ju by 7 to 9/1. According to 

 Clinton, they do not retain their vitality long. An investigation of 

 perithecial formation indicates that perithecia begin to form in 

 October, or even later, and reach maturity in the following April, 

 when mature ascospores have been 

 found especially on the under sur- 

 faces of the leaves. They are im- 

 bedded in the leaf tissues and are 

 slightly pyriform in shape, includ- 

 ing clavate slightly curved asci 

 measuring 55 to 75// by 6 to 12^1. 

 Each ascus contains eight two- 

 celled ascospores, which are olive- 

 brown in color with the following 

 dimensions: 11 to 15/iby 5 to 7/x. 

 They germinate readily in water. 

 Spraying with lime-sulphur 

 mixture 32° Beaume, 1-40, before 

 the time of flowering has been rec- 

 ommended for Scab, followed by 

 a second, or even a third spraying 

 after the petals fall, and at least 

 two or three weeks after the 

 second. 



Ash (Fraxinus americanus, L.) 



Heart-rot (Fomes fraxinophilus 

 (Pk.) Sacc). — In the Mississippi 

 Valley, white ash trees of all ages 

 are attacked by this bracket 

 fungus, which is a tree wound 

 parasite, entering usually the stub 



of a branch, which has been broken off by the wind, or by snow. From the 

 point of entrance, the mycelium grows into the heartwood of the trunk. 

 The wood at first turns darker in color, later the disease is marked 

 by a bleaching of the color in the spring wood of the annual rings, which 

 turn to a straw color and then become blanched. The whole woody 

 31 



Fig. 166. — An old sporophore of Fomes 

 (Polyporus) fraxinophilus on white ash. 

 (After Herynann von Schrenk, Bull. 32, 

 U. S. Bureau of Plant Industry. 1903.) 



