326 DISEASES OF CULTIVATED PLANTS 



leaves and young shoots, the cortex of the latter becoming 

 orange colour. Growth of the branch is arrested at the 

 infected part, whereas growth continues at other parts, and 

 the result of this unequal growth causes the shoot to become 

 more or less curved, and as the tip of the branch tends to 

 grow upwards, double or S-shaped curves are produced. 



Rostrup demonstrated by means of inoculation experiments 

 that the teleutospore condition of the fungus grows on aspen 

 leaves, and was at one time called Melampsora tremulae (Tul.) 

 The uredospore stage also develops on aspen leaves during 

 the summer, often nearly covering the surface with a yellow 

 powder. The teleutospores appear later when the leaves 

 are dead, and form dark-coloured crusts. 



Aecidiospores pale reddish-yellow, subglobose, warted, 

 15-20 /* diam. 



Uredospores elliptic or ovoid, orange, aculeate, 28-38 X 

 13-20 fjt.. Paraphyses with the apex swollen. 



Teleutospores 40-45 X 13 /*. 



Badly-diseased plants should be removed from seed-beds 

 and nurseries. Aspens should not be allowed in the 

 neighbourhood of nurseries. 



Hartig and Somerville, Diseases of Trees > p. 166. 

 Prillieux, Malad. des Planfes AgHc., i, p. 286. 



Flax rust (Melampsora lini, D. C.) sometimes proves 

 injurious to cultivated flax. It is also very common on the 

 little, wild, purging flax (Linum catharticuni). The uredo 

 stage forms orange-coloured spots on the leaves, sepals, etc., 

 and is followed by the rather large, black, shining pustules of 

 teleutospores. 



Uredospores rounded, echinulate, orange, 15-25 x 13-16 /*, 

 paraphyses capitate. 



Teleutospores cylindrico-prismatic, polygonal in section, 

 45 x 20 p. 



A difficult disease to eradicate. Burning material infected 

 with the teleutospores is the only method that can be 

 suggested. 



Melampsora repentis (Plow.). Plowright has proved by 

 cultures that the old Caeoma orchidis found on Orchis 

 maculata is an aecidium form having its uredo and teleuto- 

 spore forms on Salix repens. 



Uredospores with minutely spinulose wall, contents orange- 



