COTTON DISEASES 



415 



all other plants having tender succulent roots. Mean- 

 time the land may be cropped with any of the grains, with 

 any of the forage grasses, 

 or with peanuts, or with 

 velvet beans, or with 

 the Iron variety of cow- 

 peas, which are all 

 practically exempt from 

 attack. 



The root-knot en- 

 largements may be dis- 

 tinguished from the 

 beneficial tubercles oc- 

 curring on the roots of 

 cowpeas and other leg- 

 umes as follows: 



When small, root- 

 knot swellings are gen- 

 erally longer than thick, 

 and the swelling is on 

 all sides of the root ; 

 while tubercles are always formed on one side of the root. 



386. Boll-rot or anthracnose (Colletotrichum gossypii). 

 This fungus is responsible for the greater part of the rot- 

 ting of the bolls of cotton. In its worst form, which occurs 

 during damp weather, small discolored depressions appear 

 on the bolls ; these spots become grayish and in time be- 

 come covered with pinkish spores, which in effect are the 

 seedlike parts of the fungus (Fig. 183). Either a single lock 

 or the entire contents of the boll may be rotted. Or the 

 disease may keep the boll from opening widely. 



FIG. 



182. ROOT-KNOT OR NEMATODE 

 INJURIES ON COTTON ROOTS. 



