450 



BOTANY OF THE LIVING PLANT 



USTILAGINEAE (SMUTS). 



The Smut-Fungi (Ustilagineae) are also parasites on Grasses, 

 certain of them causing diseases on Oats, Barley, Wheat, and Maize, 

 which culminate in the fruiting Ear. The diseased grain is replaced 

 by a mass of dusky spores, corresponding in their behaviour to the 

 teleuto-spores of the Uredineae (Fig. 385). For like them they 

 germinate after the winter's rest, forming a basidium (promycelium) 

 with infective carpospores (sporidia). These have been shown to 

 be able to infect the seedlings of the corn-plants. The spores may 



.T1U. ^00- 



Spores of Ustilago germinating, and giving off sporidia. (a) germinated in w 

 only, b, c, d, e in nutritive solutions, where they continue to sprout. Very hij 

 magnified. (After Brefeld, from Marshall Ward.) 



r ater 

 y highly 



have remained on the soil in the field from the previous season ; 

 or the crop may have been harvested, and the straw used for bedding, 

 passed to the manure-heap, and then carted out on to the land again. 

 Either way the soil in which the grain germinates will have been 

 infected. A further point of importance is that in a nutritive fluid, 

 like the foul water of the manure-heap, the carpospores formed on 

 germination continue to multiply by sprouting like yeast, thus increas- 

 ing the chances of infection (Fig. 385, d, e) . It is only the seedling corn 

 that can be infected. The plant once infected grows on as though 

 quite healthy till the flowering period. Then the parasite, the 

 mycelium of which has followed its growth internally, fastens on 

 the ovary, where nutritive material is concentrated, and diverts 

 the food from the formation of the grain to the nutrition of a mass 

 of its own spores. For prevention of the disease " dressing " of 

 the seed-grain with disinfecting mixtures is practised. But equally 



