386 



TEXTBOOK OF BOTANY 



Fig. 219. 



dark portion of the figure repre- 

 sents masses of escaping spores. 



the com smut are sometimes as 



large as a man's fist ; tiiey 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 



A smutted ear of §'"0^ between the cells of the 



corn. Notice the immense size host plant and send branches 



of the diseased kernels. The ^^^^ ^-^^ ^^gij^ ^q 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 verj^ short cells which be- 

 come dark, thick-walled winter spores. 

 These spores ma}' 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 com plant 

 cause a new infection. The com smut 

 affects only the tissues in the neighbor- 



FiG. 220. — ^, a germi- 

 nated winter spore of the 



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



only method known for controlling ^^'"^^ S™'^^ from the 



,1-1. . , 1 1 , spore, and the small 



this disease is to remove and destroy .po^^^ (sporidia) which 



all the swellings before the winter this plant bears. 



spores are formed. 



B, a 

 single sporidium. C, a 

 ™, , J r , sporidium which is bud- 



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

 infect the oat plant only when it is a ium. 



