18 



MICROBES, FERMENTS, AND MOULDS. 



it cannot be regarded as fit for food. The dust 

 arising from these fungi often produces in threshers 

 in a barn an irritating cough, which ceases when 

 they are no longer subject to the exciting cause. 



The verdet, or, as the Italians call it, verderame of 

 maize is due to the presence of the same parasite 

 (Ustilago segetum, Uredo carlo, or Sporisorium mazdis) 

 on the grains of maize, and for a long while it was 

 believed to produce pellagra, a common disease among 

 the peasants who live on maize. It is now known 

 that pellagra is due to the growth of another fungus, 

 much resembling the ergot of rye, of 

 which we shall speak presently. 



Other species of Uredinece attack 

 sorghum, rice, etc., and, indeed, very 

 many plants are affected by parasitic 

 fungi belonging to the genus Puccinia 

 and to allied genera, and it is probable 

 that they almost all present the phe- 

 nomenonxof alternation of generations. 

 A simple means of freeing our fields from the rust 

 of wheat is indicated by what we now know of the 

 alternation of generations which ensures the propaga- 

 tion of this fungus. We must destroy all the barberry 

 bushes which are found in the vicinity of cornfields. 

 Popular opinion, although ignorant of the phenomenon 

 of alternation of generations, has long regarded the 

 neighbourhood of the barberry as the principal cause 

 of the rust of cereals. 



Fig. 7. gpores of 

 Uredo rubigo vera, 

 or Puccinia coro- 

 nata. 



