40 



FUNGOID DISEASES 



Ca7ise. — Examined under the microscope the 

 above brown powder is found to consist of myriads 

 of spores (chlamydospores or teliospores) of the 

 fungus Ustilago AvencB. 



Each spore is rounded and has two coats, but the 

 spores are free from the fishy odour which accom- 



A B 



Fig. 8. — Oat smut {Ustilago Aveim) : (A) Portion of healthy ear of oats; 

 (B) Portion of smutted ear ; notice that the spikelets are very irregular 

 in shape and blackened with the spores of the fungus. 



panics the spores of bunt (see p. 47). The spores 

 germinate readily in water, and dung heaps also 

 form a suitable medium for arowth. 



Since the spores are distributed before harvest, 

 some are blown on to the healthy ears, but no de- 

 velopment takes place until the grain is sown the 

 following spring. The grain and the spore germin- 



