CONIOTHYRIUM 415 



Hellebore leaf blotch. Large, circular, brownish blotches 

 formed, showing on both surfaces of living leaves of Helkborus 

 niger, and may probably occur on other species. The blotches 

 have a scorched appearance, and are studded with the minute 

 blackish perithecia which are usually arranged in rings. 

 Spores oval, pale brown, 4-5x2-3 /x. The parasite is called 

 Coniothyrium hellebori (Cooke and Massee). 



Cut off and burn infected leaves. 



Yucca leaf blotch {Coniothyrium concentricum, Sacc.) 

 forms greyish more or less circular dead patches, ranging 

 from 1-3 cm. diam., on the living leaves of species of Yucca, 

 Agave and Fourcroya. The minute blackish perithecia are 

 often arranged in concentric circles on the dead spots, but 

 not always. The spots themselves are frequently bounded by 

 a darker brown line. Spores subglobose, becoming dark 

 coloured, 4-5 X 3-4 \>-. 



Diseased leaves should be cut out, otherwise the fungus 

 extends rapidly and causes much disfigurement. 



Rose canker. Large, irregular, cankered wounds are 

 frequently met with on the stems of both wild and cultivated 

 roses; their presence is due to Coniothyrium Fuckelii (Sacc), 

 which is considered by some as a conidial condition of 

 Leptosphaeria coniothyrium (Sacc). The disease commences 

 on one-year-old wood, and its presence is revealed by small 

 reddish patches scattered over the green bark. At a later 

 stage, minute cracks appear at the injured points, and 

 gradually continue to increase in size. At this stage the 

 formation of callus begins, the cells of which are in turn 

 attacked by the fungus, consequently the callus continues to 

 grow and form large nodulose masses which may extend for 

 many inches along the branch, forming the well-known canker. 



If the irregular outgrowth forming a cankered spot is 

 examined with a pocket-lens, numerous, very minute black 

 dots will be seen ; these are the fruit of the fungus. It is 

 considered that frost aids in the formation of canker, after 

 the fungus has first made a start. The fungus is a wound- 

 parasite, the spores gaining access to the living tissue through 

 small wounds made by the spines of the plant itself, when 

 one branch is blown against another by wind, by insects, etc 



Perithecia black, depressed, scattered, 180-200 ji diam., 

 spores minute, very numerous, 3-4 X 2-3 p. 



