338 



DISEASES OF CULTIVATED PLANTS 



forming fantastic curves. Aecidia fleshy, crowded, pale flesh- 

 colour, spores angularly globose, orange-red. 



USTILAGINACEAE 



All the members of the present group are obligate parasites. 

 In many instances the spores are produced in the ovary, often 

 on the leaves, sometimes in the anthers. The spore pustules 

 form sooty, black powdery masses when mature, and are 



Fig. ioo. Germinating spores of species of Ustilaginaceae. 

 i, Ustilago arundinellae \ 2, Txlletia decipiens, the secondary 

 spores producing tertiary spores ; 3, Tillelta tonata. All highly 

 mag. (After Brefeld. ) 



known as 'smuts' and 'bunts.' Teleutospores only are 

 known in this group. 



In some instances infection takes place in the earliest seed- 

 ling stage of the host-plant, the spores being present in the 

 soil, or adhering to the seed when sown, as in oats. In 

 other instances infection occurs in the flower, spores being 

 deposited on the stigma, and a mycelium is found in the 

 ovary, as in wheat. In maize, on the other hand, infection 

 can take place during any age, so long as young tissue is 

 present. The teleutospores on germination produce a pro- 

 mvcelium which gives origin to secondary spores ; these in 

 turn often germinate and bear a third form of spore. In 

 Ustilago the spores on germination produce minute secondary 

 spores which increase in number by gemmation or budding, 



