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Make a diagrammatic DRAWING showing the structure of the spore-ball. 
If no germinating spores are available, sketch the illustration shown in 
the above reference. 
Cut a cross-section of an onion seedling through a closed lesion or use 
prepared slides. OBSERVE :— 
8. The depth to which the sorus penetrates. 
9. The black mass of spores lining the sorus. Are they attached 
to stalks? How are the spores of a smut-pathogene usually borne? (See 
McAlpine, Smuts of Australia, p. 19.) 
10. The cuticle still intact and retaining the spores which later 
escape. 
11. The mycelium penetrating the tissues adjoining the sorus. 
Do any of these cells appear dead? 
Make a DRAWING of a cross-section of a sorus with the host-tissue 
surrounding it. 
Saprogenesis. There is no vegetative activity during saprogenesis. 
The spores lie dormant in the soil or host-debris. They have been known. 
to live over in the soil as long as twelve years. 
Secondary cycle. Unlike most fungi this pathogene has no secondary 
cycle. Infection takes place only during a limited period while the host 
is in the seedling stage. They are initiated only by overwintered spores. 
Consequently, even if onion sets are transplanted to badly infested soil, 
the onions will remain free from the disease. 
REPORT 
1. Discuss the use of sulphur and of formaldehyde in the control 
of this disease, including the advantages or disadvantages in methods of 
application, the amounts used, cost, and the preference of the onion- 
grower of the present day. 
