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 carbo, or Sporisorium maidis) 
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 Uredinee attack 
sorghum, rice, etc., and, indeed, very 
many plants are affected by parasitic 
fungi belonging to the genus Puccinia 
ee rey and to allied genera, and it is probable 
Uredo rubigo ver that they almost all present the phe- 
am ‘nomenon-of 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. 
