508 SPECIAL PLANT PATHOLOGY 



The greatest pains should be taken to secure only sound seed corn, 

 but in the present indififerent state of the seed-trade, even the best 

 should be treated with mercuric chloride before planting. On fields 

 subject to the disease, only resistant varieties should be planted. 

 Manure containing corn stalks from diseased fields, or gathered from 

 animals pastured in such fields, should never be used on land designed 

 for corn.^ 



Cotton (Gossypium sp.) 



Boll Anthracnose (Glomerella gossypii (Southw.) Edg.) (= Colleto- 

 trichum gossypii, Southw.),- — The same fungus causes an anthracnose 

 of stem and boll of the cotton plant, especially in the Gulf states. The 

 disease is more important when it attacks the boll, or the seedlings. 

 The ^bolls lose their green color and become dull red, or bronzed. 

 If the boll is nearly- mature when attacked, it may mature and 

 open in the usual manner, but if attacked early, it may cause a prema- 

 ture dying of the carpels and an unequal growth of the boll, which is 

 liable to crack open and expose the immature lint to the action of the 

 weather. The first evidence of the disease is a minute reddish spot, 

 which later becomes black in the center and depressed with a reddish 

 border, and these spots may run together. 



Two types of conidiophores break out from the stroma within the 

 tissues. Some of the conidiophores are hyaline and abstrict conidio- 

 spores that measure 4.5 to 7^1 by 15 to 20/x, while other conidiophores in 

 the form of setae arise from the dark colored cells of the stroma. The 

 setse are clustered and bear ovate, basally pointed spores. Spores and 

 setae together form an acervulus. The spores germinate readily and 

 produce a myceUum which grows vigorously in culture, is hyahne, 

 flexuous and abundantly septate and it may give rise to appressoria. 



Proper remedial measures have not been discovered, and a field of 

 experimentation is opened up along these lines. Use resistant 

 varieties. 



Rust (Uredo gossypii, Lager.). — This is the uredo stage of Kuehneola 

 gossypii (Lagerh.) Arth. which occurs on the cotton plant in Cuba, 

 Puerto Rico, Florida and Guiana, ^cia are wanting in the life cycle, 



1 Smith, Erwin F. : Bacteria in Relation to Plant Diseases, Volume III: 89-150, 

 1914,^ where full details of the experimental study of the disease and the causal 

 organism will be found. 



