CANKER IN WHEAT. 219 



772. There is a disease known by the name of blight, 

 canker, smut-ball, pepper-brand, &c., which is often 

 confounded with smut, but really very different. It has 

 been supposed to be a fungus in the seeds of wheat, by 

 means of which the farina was replaced by a whitish 

 substance which finally became a fine powder, 



the outside or skin of the seed being untouched, 

 and giving no signs of the presence of the disease. 

 Figure 47 shows a section of a cankered grain 



f i Fig. 47. 



of wheat. 



773. But more recent investigations indicate that it is 

 caused by microscopic animalcules or thread worms, which 

 possess the remarkable power of remaining perfectly dry 

 and hard for years, and then regaining life and motion 

 when moistened. 



774. Grain affected by this disease, becomes a hard 

 shell filled with powder, which is usually white. This 

 powder has no trace of starch, but is composed entirely 

 of microscopic threads, which are stiff, dry, hard worms. 

 When found in new grain, if placed in water, they show 

 signs of life very quickly. If very old, it requires many 

 hours or even days to revive them. Several thousand 

 of these worms may be found in a single kernel. 



775. When these diseased grains are sown with sound, 

 the moisture gradually revives the worms. They break 

 through the thin shell of their prison, and seek the 

 young shoots of the wheat which has germinated, are 

 carried up by the growth of the plant, or, if the 

 weather be wet, by their own exertions, effect a lodgment 

 in the young kernel, and lay their eggs there. 



776. At the time of the ripening of the grain the 

 parent worms are dead, the shells of the innumerable 

 eggs which have produced larvae have been absorbed, and 



