28o Diseases of Greenhouse Crops 



With the advance of the disease, the spots become 

 coated with a fuzzy, brownish coat, made up of 

 the fruiting stalks. As the plant becomes decayed, 

 numerous sclerotia appear. The disease is spread in 

 the hothouse through the watering or in syringing. 

 Infection is favored by a high humidity and poor 

 light conditions in the house. Little is known of 

 the causal organism (fig. 58, d.). 



Control. The disease may be kept in check by 

 proper ventilation. 



Calla Lily (^Aracea spp.") 



Cultural Considerations. The yellow callas are 

 grown in the same way as the white callas except 

 that they seem to do better without a rest period. 

 White callas require a rich soil, full simlight and 

 an abundance of water during the growing season. 

 During the summer, the plants undergo a resting 

 period. The pots are laid out in the open in the 

 shade and a little water is given occasionally to pre- 

 vent the Rhizomes from drying out. 



Diseases of the Calla Lily 



Callas are apparently a hardy plant. It is sub- 

 ject to but few diseases. 



Soft Rot 



Caused by Bacillus aroidea Town. 



Symptoms. This disease may be foimd both on 



