Lily Diseases 281 



calla lilies in the greenhouse or in the field. The 

 callas usually rot off at or below the surface of the 

 ground, the disease frequently spreading downward 

 in the direction of the corms and upward into the 

 leaves. Occasionally soft rot starts at the edges 

 of the leaves or at the flower stalk. The disease 

 spreads more rapidly and is also worse in green- 

 houses where callas are grown in solid beds. 



In cutting open a diseased corm, one observes a 

 line of demarkation between the healthy and dis- 

 eased tissue, the latter being brown, soft, and water 

 soaked. Affected leaves become slimy without nec- 

 essarily losing their green color. If the disease at- 

 tacks flower stalks, the flowers turn brown and the 

 stalk falls over although its green color is preserved. 

 As the disease progresses under ground the plant 

 above ground topples over without any sign of dis- 

 ease. Under unfavorable conditions, the disease in 

 the corm may not progress further than a small spot 

 which soon dries. The causal organism, however, 

 remains alive in these spots, but dormant until the 

 time when conditions of moisture and temperature 

 again become favorable. The nature of the soil de- 

 termines to a large extent the severity of the rot. A 

 soil rich in humus is most favorable for its spread. 



The Organism. Bacillus aroidea is a short rod 

 with rounded ends, single or in chains of two or four. 

 Its growth is white on solid media. It produces no 

 gas, and liquefies gelatin. Although apparently dis- 

 tinct from Bacillus caratovorus Jones, it is neverthe- 

 less capable of producing a soft dark colored rot in 



