The spore-bearing pustules of the fungus appear on the 

 diseased area in the form of orange-coloured spots which 

 are frequently arranged in concentric rings. The fungus 

 makes its entrance through the stomata or by means of 

 wounds. 



Diagnosis. — Spots circular or elliptical, often becoming 

 confluent, olive, changing to grey or brown ; acervuli 

 spherical to oblong, usually breaking through the epidermis 

 in concentric rings and ejecting orange-coloured masses of 

 conidia ; setae acute to blunt, light-brown, 3-5-septate, 

 1 10-170 by 5-6 microns; conidia oblong to cylindrical, 

 hyaline, with one or two guttules, 16-31 by 5-6 microns ; 

 conidiophores erect, hyaline, usually simple, 6-J microns 

 broad, but very variable in length in different acervuli. 



G. G. HEDGCOCK : Sixteenth Ann. Report, Missouri 

 Botanical Garden, p. 1 5 3- 



COLLETOTRICHUM GOSSYPII, Southw. 

 (Anthracnose of Cotton.) 



The fruits, stem and leaves of the plant are attacked by 

 this fungus, but the most serious damage is done when it 

 affects the fruits, a loss of as much as 50 per cent, of the 

 crop has been recorded in Alabama, U.S.A. 



Minute, reddish-brown spots appear on the " bolls " ; 

 these spots increase in size and the inner part of each 

 blackens, the margin remaining reddish-brown. Pustules 

 appear in the centre of the spot and give it a grey or pink 

 colour. 



Attacked fruits do not mature properly, they usually 

 become dry and die without opening, or they open only 

 slightly at the top. 



In some cases the stems of seedling plants are attacked, 

 the fungus affecting that part of the stem which is just 

 above ground, and the plant withers and dies as if it were 

 " damping off." Such leaves as have become in some way 

 weakened are those which are usually attacked. 



The careful selection of non-infected seeds for planting 

 and the soaking of seeds in a one per cent, solution of 

 mercuric chloride for one hour have given good results. 



Good results should also attend the raising of resistant 

 varieties. 



Diagnosis : Sori orbicular, dark-coloured or covered with 

 a pink powder ; acervuli erumpent ; conidia irregularly 

 oblong, hyaline, flesh-coloured in mass, 11-20 by 4"5 _ 5"5 



48 



