PESTS OF THE FLOWER GARDEN. 



27 



American Spot Disease. 

 Alternaria Viola (Gall.), PL II. fig. 25. 



There is very little doubt that this disease has made its appearance in 

 this country, and is capable of doing considerable damage. It occurs 

 principally on the leaves, commencing with small yellowish spots, sur- 

 rounded by a narrow rim ; sometimes they spread till they occupy the 

 whole leaf. Most of the spots are free from fungus spores, with scarcely 

 any indications of mycelium. Spores are developed in a saturated atmo- 

 sphere after twenty-four hours. 



The spores are borne in chains, or darkish-brown threads, which rise 

 from the diseased surface. They separate easily, and can be transported 

 freely to other and healthy leaves. These spores, or conidia, are club- 

 shaped, or flask-shaped, divided by transverse as well as vertical septa, so 

 as to be muriform (40-60 xl0-17ju), somewhat olive in colour. 



Hitherto known only in the United States and in Britain, it is 

 undoubtedly a dangerous pest. 



At present no effective remedy has been discovered. Fungicides have 

 produced little or no effect. Suggestions are made as to prevention, 

 rather than cure, by giving careful attention to the production of vigorous, 

 healthy plants. 



Healthy plants inoculated with the fungus spores soon produced the 

 disease. 



U.S.A. Dep. Agric. Bull. 23, 1900 ; Journ. Boy. Hort. Soc. xxvi. 

 December 1901, p. 246, pp. 491-3 ; xxvi. 1902, p. ccxxii. 



Italian Violet Black Mould. 

 Macrosporium Violce. 



A black mould, under the above name, of which we have no descrip- 

 tion up to now, is reported to be destructive to Violets in Italy. 



At the time of going to press we have seen Violets with the leaves in 

 a bad condition, but there is no evidence that such condition has been 

 caused by a parasite. The tissue was entirely bleached and dead over a 

 large portion of the surface, commencing at the margin, and extending 

 inwards, and not interfoliary. Cultivators are of opinion that it is due to 

 external circumstances, which is most probable. 



All the dead spots seen by us become occupied by tufts of black mould, 

 which are not present when the fading commences, but occur only on the 

 dead tissue, and hence it is probably a saprophyte. 



The moulds are of two kinds, growing in company, forming small 

 dark olive tufts, and not becoming confluent. The earliest form is a 

 Cladosporium, with slender unbranched septate threads of a pale olive 

 and rather long. The conidia at first continuous, then uniseptate, at 

 length bi- or tri-septate (18-30x7 /i). 



The other mould, which appears mixed with the former, is a Macro- 

 sporium resembling M. sarcinula, with delicate deciduous threads and 

 somewhat cubical conidia (30-35 x 25-30 n). Truncate at the ends and 

 but slightly constricted. The septa, longitudinal and transverse, divide 

 the conidia into quadrangular cells, mostly in three irregular rows, and of 

 a darker olive brown than the Claclosporium. 



