FOOD 



163 



The grain in course of time gets converted into a black or 

 olive-coloured greasy powder, of a fishy objectionable 

 odour. 



Smut (Fig. 26) is a disease which attacks the flowering 

 heads of grasses and grains, 

 more particularly, wheat, bar- 

 ley, oats, and rye. It com- 

 mences as a white deposit, 

 but later turns to a black 

 mass. This consists of spores 

 of the fungus Ustilago carbo. 

 The effect of this fungus is to 

 completely destroy the flower- 

 ing head, so that the whole 

 ear disappears and nothing 

 but its framework is left. The 

 disease is very readily de- 

 tected, and unlike Bunt it has 

 no odour. 



Rust and Mildew are pro- 

 duced by different stages of 

 the same parasite, known as 

 Puccinia graminis (Fig. 27). 

 It affects all grasses and 

 cereals, and is an extremely 

 serious disease from an agri- 

 cultural point of view. 



The life history of the para- 

 site is complex and interest- 

 ing, it requires to pass through 

 two different host plants in 

 order to complete the cycle of 

 its existence, and in each host it produces a distinct 

 disease; in fact, its behaviour is more like that of an 

 animal parasite. 



The stems and leaves of all grasses and cereals are liable 

 to be attacked in the early summer by yellowish-red lines 



* ' Elements of Agriculture.' 



11—2 



Fig. 26.— Smut of Oats (Fream).* 

 A, panicle of oats attacked from 

 below upwards ; B, spikelet with 

 the fungus in an early stage of 

 growth ; C, free spores of Ustilago 

 carho ; D, spores germinating and 

 producing yeast-like buds. 



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