ROOT CROPS. 



45 



ramifies chiefly in the upper part of tte bulb, causing 

 decay. Among this mycelium are numbers of black grains 

 — the sclerotia, or masses of mycelia in a resting state. 

 Each sclerotium germinates by throwing out hyphse which 

 ultimately give rise (at their ends) to sporangia containing 

 oval sporidia (spores). The sporangia, when ripe, burst in 

 the air, and the spores are wafted about by air currents, 

 causing destruction to crops of onions. The spores ger- 



Fig. 18. — "Garlic Bust" {Fuccinia mixta). 



A. Flower stalk (frd nat. size) showing the disease " pustules" or sori. 

 J-t. The same x 4 diameters. . 



C. Transverse section of small sorus. The epidermis of host-plant is brokeu 



at 3 and 4, by the fungus whose mycelium is thickly matted amongst 



the tissues of host. 



1 and 2 show the two kinds of spores x 75. 



minate on the host-plant, giving rise to hyphse, mycelia, and 

 sclerotia. The latter are capable of retaining their vitality 

 through the winter months, and germinate in the spring. 



Prevention. — (1) Burn all infested onion refuse. (2) 

 Autumn sowing. 



The Garlic Rust {Fuccinia mixta, Fig. 18) was 



