I37S 



DISEASES OF VARIOUS CROPS 



and of variable dimensions: ig.'S — ■ 33 X 4.95 — 6.6 [x. The conidiophores 

 are unicellular, colourless, with rich content of protoplasm and measure 

 6.16 — 10.75 X 1.54 — 1.55 [JL. The spores are of low resistance power, and 

 although they are able to pass through the alimentary canal of animals 

 without undergoing apparent deterioration, their vitality is nevertheless 

 greatly impaired; exposure to the sun delays their germination ; the germina- 

 tion capacity dies out entirely in spores one year old. The writer has stud- 

 ied the growth of spores under anaerobic conditions, with various degrees 

 of alkalinity and acidity, after exposing them for 2 hours to the action of 

 freezing mixtures. In plain agar the fungus grows little. On the other hand, 

 if a little oat flour is added to the agar a rich growth occurs. Among the 

 fungicides examined the best results were obtained with lithium salts, which 

 stop the growth of the mAxelium and prevent the germination of the spores. 



As means of control against dry rot it is advised : i) to remove from 

 the fields and destroy by fire all vegetable residue which, if left there, would 

 become centres of infection ; 2) to discontinue maize-growing for some 

 years in the infected zones, and also in the adjoining fields. 



As was stated above, the diseased caryopses are distinguished by their 

 light weight which is brought out clearly by the following table : 



Weight of ear 

 without bracts 



I^cnoth of ear 



Weight of caryopses | Weight of raehis 



The average loss of weight of the caryopses is therefore 27.8^0, and, 

 in serious cases, it may even amount to 50 %. 



The alteration of the grains is due largely to the action of a diastatic 

 enzyme secreted by the mycelium of Diplodia, which attacks and destroys 

 the embryo and the starch grains. 



Another enzyme afterwards separates the fatty substances, which ac- 

 counts for the reduction in the fat content in the infected maize. When 

 fed to livestock the latter does not cause any poisoning but the deteriora- 

 tion in its composition really does not make it a food to be recommended. 



