DETAILED ACCOUNT OF SPECIFIC DISEASES OF PLANTS 483 



tissue becomes straw-colored and finally transformed into a loose 

 spongy mass of fibers, which readily absorbs water (Fig. 167). 



The fruiting brackets, or sporophores, make their appearance from 

 the mycelium at the base of the stubs, or from wounded surfaces, 

 either alone, or a number together (Fig. 166). The mature sporophore, 

 according to von Schrenk,^ is nearly triangular in cross-section with a 

 broad rounded edge, which at first is white, turning gradually darker 

 until it becomes straw-colored (Fig. 167). The older portions of the 

 upper surface are dark brown, or black, and are very hard and woody, 

 its upper surfaces obscurely zoned, pale brown and rust colored. Wound 

 protection, as outlined in the section on prophylaxis, is an important 

 method of preventing the white heart-rot from killing white ash trees. 



Asparagus (Asparagus officinalis, L.) 



Rust {Puccinia asparagi DC.) — The asparagus rust is well-known, 

 having been investigated by a number of mycologists in this country, 

 notably Halsted, Sirrine, Smith and Stone. ^ In Europe the disease is 

 of little consequence, but in America it threatens the asparagus growing 

 of our country, spreading rapidly, especially during times when dew is 

 abundant, for Smith says: "The amount of rust varies directly and 

 exactly with the amount of dew, and so long as there is little or no dew, 

 there can be no rust." During dry summers rust is largely absent. 



All of the spore forms are found on the stems and twigs of the culti- 

 vated asparagus and on several wild species of the genus. The uredi- 

 nia and telia appear also on the leaf-like branches of the plant. The 

 aecidia appear as long light-green cushion-like patches. They have a 

 white peridium and are short cylindric, inclosing the orange-colored 

 aeciospores, which are 15 to iS/z in diameter, and retain their power of 

 germination for several weeks. Stomatal infection probably is the rule. 

 Associated with these secia are spermagonia in small, yellow clusters. 

 Early summer ushers in the red rust (uredo) stage of the disease with 

 the deep brown sori more or less scattered at first, later becoming con- 

 fluent. The urediniospores are yellowish-brown, thick-walled with 

 four germ pores and measure 21 to 24^. The clothing of a person 



Won Schrenk, Hermann and Spaulding, Perley: Diseases of Deciduous 

 Forest Trees. Bull. 149, U. S. Bureau of Plant Industry. 



''Smith, Ralph E.: Asparagus and Asparagus Rust in California. Calif. Agric. 

 Exper. Sta., Bull. 165: 1-95, 1905. 



