8 TIMOTHY RUST IN THE UNITED STATES. 



DESCRIPTION OF TIMOTHY RUST. 



The timothy rust is very similar in general appearance and mor- 

 phological characteristics to Puccinia graminis Pers. on wheat. It 

 attacks both leaf and stem, forming long, yellowish-brown uredo 

 pustules and dark-brown to black teleuto pustules, which rupture the 

 epidermis. At times it also attacks the head, often preventing the 

 formation of seed. The uredospores are most prevalent, while the 

 teleutospores are less abundant. 



The uredospores are 18 to 27// in length and 15 to 19/t in width; 

 the teleutospores, 38 to 52 /« in length and 14 to 16 ,« in width. This is 

 the same range as that of the corresponding spores of Puccinia 

 graminis Pers. on wheat, but the variation is not quite as great as in 

 the wheat rust. The teleutospores are constricted in the middle and 

 have a much thickened, round or pointed apex and pedicels of 

 medium length, and closely resemble those of the typical Puccinia 

 graminis Pers. 



RELATIONSHIP AND PHYSIOLOGICAL SPECIALIZATION OF 



TIMOTHY RUST. 



In 1908 and 1909 inoculation experiments on various grasses were 

 undertaken at Washington, D. C, to determine the relationship of 

 the rust of timothy to rusts of other hosts in this country and to 

 ascertain whether or not it is the same form as that wliich occurs in 

 Europe. Collections were made at the Arlington Experimental 

 Farm, and fi'esh material in the uredo stage was kept gromng in the 

 greenhouses at Washington, D. C. AU inoculations were made on 

 young, fresh leaves of the host plants growing in pots. The plants 

 were kept moist for 48 hours after inoculation by placing the pots in 

 moist chambers consisting of large bell jars placed in pans containing 

 sand and a little water. In this way a thin film of water soon con- 

 densed on the leaves and remained as long as the plants were covered. 

 This gave ideal conditions for spore germination and for infection. 

 The results of these inoculations are reported in Table I. 



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