502 SPECIAL PLANT PATHOLOGY 



the pustules.' All of the experiments point to air and wind transport 

 of the ascospores, as one of the very important methods of dissemina- 

 tion. Infection is by means of wounds produced mechanically, as by 

 insects and other animals (Fig. 178). It is still to be demonstrated that 

 the parasite can enter without visible breaks in the bark.^ In the 

 control of this disease inspection of nursery stock should be made 

 and the use of gas tar following renioval of diseased branches. 



Leaf Mildew {Phyllactinia corylea (Pers.), Korst). — ^The under leaf 

 surfaces of the chestnut are marked frequently by irregular patches 

 of mycelium, which constitute the mildew fungus (Fig. 53). Typical 

 haustoria are absent, but there are special setalike branches which 

 penetrate the leaf tissues. The subglobose perithecium is large and 

 is garnished with rigid needle-like appendages with a swollen base 

 (Fig. 53). There are many included asci usually containing two 

 spores, occasionally three. It is a fungus of wide geographic distribu- 

 tion throughout the temperate regions of the world. 



Clover {TrifoUum spp.) 



Rust, Uromyces trifolii (Hedw.), Liv. — The common clovers of our 

 cultivated fields, such as the red clover, alsike clover, white clover, and 

 crimson clover, are attacked by this rust, which causes serious disease 

 conditions (Fig. 70, E and F). The prevalence of the disease varies 

 greatly with the season. The clover rust fungus is autcecious, all of 

 the stages being found on the same host plant. All of the stages 

 occur on the white clover {T. rep ens). In general the spermagOnia 

 and aecia are not met with on the red clover, the host upon which the 

 other stages are perhaps more frequent. The mycelium is local in its 

 occurrence in the plant, from it a:cia and spermagonia arise in the early 

 spring, or at almost any time during an open winter. They occur on 

 the under leaf surfaces and on the leaf stalk. The aeciospores are 14 

 to 23/< in diameter and germinate readily in water. 



Heald, F. D., Gardner, M. W. and Studthalter, R. A.. Air and Wind 

 Dissemination of Ascospores of the Chestnut Blight Fungus. Journal of Agricul- 

 tural Research iii: 493-326, March 2s, 1916. 



'For numerous other details consult Anderson, P. J. and Rankin, W. H.: 

 Endothia Canker of Chestnut. Bull. 347, Cornell University Agricultural Experi- 

 ment Station, June, 1914. 



