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TEXTBOOK OF BOTANY 



corn. Notice the immense size 

 of the diseased kernels. The 

 dark portion of the figure repre- 

 sents masses of escaping spores. 



the corn smut are sometimes as 

 large as a man's fist ; they occur 

 on the stem, leaves, or roots, in 

 the ears or in the tassels. A 

 large part of an ear, or even a 

 whole ear, may be replaced by 

 the black masses. The fungus 

 that causes the disease is made 

 up of branching threads which 



FIG. 219. -A smutted ear of grow between the cells of the 

 host plant and send branches 

 into the cells to obtain food. 

 The fungus does not kill the 

 host cells at once ; on the con- 

 trary, it stimulates many of them to rapid growth and 

 division, thus causing the appearance 

 of a swelling. The host cells are finally 

 killed, and then the fungous threads 

 divide into very short cells which be- 

 come dark, thick-walled winter spores. 

 These spores may germinate in any 

 moist place, producing a short, thread- 

 like plant of four or five cells, each of 

 which in turn may give rise to small 

 thin-walled spores (sporidia), which 

 when they are carried to a corn plant 



cause a new infection. The corn smut 



~. , . , FIG. 220. .- 



affects only the tissues in the neighbor- nated winter spore of the 



hood of its place of entrance. The corn smut, the short plant 

 only method known for -controlling hi _ ch f s ^ rom the 

 this disease is to remove and destroy 

 all the swellings before the winter this plant bears, 

 spores are 'formed. *"& sporidium. C a 



_, . spondium which is bud- 



The common loose smut of oats can ding to form a new sporid- 

 infect the oat plant only when it is a ium. 



and the small 

 (sporidia) which 

 B, a 



