PLANT DISEASES 385 



and by their means the disease spreads rapidly. The 

 shriveled fruits lie on the ground, and the next spring portions 

 of the fungous body which have remained within them begin 

 to grow again and produce the spore sacs. Until a few years 

 ago this fungus was known only in North America, but now 

 it is reported as doing considerable damage to grapes in 

 southern Europe. Cleanliness in the orchard, the removal 

 of all diseased portions of the plants, and spraying with the 

 Bordeaux mixture, will almost eliminate the disease. 



389. Chestnut Blight, or Bark Disease of the Chestnut. 

 This disease has been known for only a few years, but it 

 threatens to destroy every chestnut tree in the United 

 States. The damage already done is estimated at from 

 $60,000,000 to $75,000,000, and no remedy so far tried has 

 been of any avail. The government authorities, with aid 

 from various states, are making efforts to eradicate the dis- 

 ease, but it has obtained such a start in some regions that all 

 hope of saving the forests has been given up. The fungus 

 grows in the outer layers of twigs, stems, and trunks, and 

 gradually kills the tissues around the part affected ; this 

 causes the death of all the parts of the tree above the dis- 

 eased region. The diseased parts show a characteristic light 

 brown color, but before long all the affected tissues shrivel. 

 Through the cracks thus produced, as well as through the 

 natural openings in the bark, short branches of the fungus 

 grow outward and produce spores which spread the disease. 

 Spores produced in sacs appear during the autumn ; but the 

 spore sacs may continue to be formed for a long time, some 

 having been obtained from tissues eighteen months after 

 the diseased condition was first noticed. A Japanese chest- 

 nut seems to be immune to the disease, and efforts are being 

 made to secure hybrid forms which may also be immune. 



390. Smuts. These very common diseases produce 

 black, powdery masses upon the Indian corn and upon 

 various other grains and grasses. The swellings, caused by 



