2o8 Diseases of Greenhouse Crops 



the variety. In form, the florets of the corolla be- 

 come elongated, tubular, with short lobes at the 

 ends. The stamens have a tendency to abort, the 

 anthers are undersized, producing little or no pol- 

 len. The pistil tends to elongate, the stigma too 

 becomes much elongated and enlarged, protruding 

 abnormally from the corolla tube. The ovary and 

 ovules too are elongated and enlarged (fig. 42, a and 

 b). Affected plants produce no seeds. The same 

 disease also attacks the Marguerite, the Calendula, 

 and the African Marigold. The cause of the trouble 

 is unknown. Practically all varieties of asters are 

 equally susceptible. The source of the seed, its stor- 

 age conditions, transplanting, the ph3^ical proper- 

 ties of the soil, are not apparently concerned in the 

 development of this malady. 



Control. It is very likely that yellows may have 

 an origin similar to that of mosaic. In the latter 

 case, insects are likely to carry and to spread the 

 virus. The control of all insect pests is therefore 

 recommended. Diseased plants should be pulled 

 out and destroyed by fire. Spraying will be of no 

 benefit. 



Leaf Blight 



Caused by Bacillus asteracearum Pava. 

 The disease is known to occur in Italy where it 

 was described by Pavarino.* The trouble is ap- 



•Pavarino, G. L., Atti. R. Accad. Lencei Rend. CI. Sci. Fis, 

 Mat. et Nat. 21 : 544-546, 1912. 



