46 VEGETABLE SUBSTANCES. 



the evil, which they called rubigo, was under the 

 control of a particular deity named Rubigus, to 

 propitiate whom in favour of their crops sacrifices 

 were continually offered. 



Blight and mildew have been very much con- 

 founded together by different writers on agricultural 

 subjects, so as to render it doubtful to which class 

 of appearances each name should in strictness be 

 applied, or whether indeed both are not applicable 

 to one and the same disorder occurring at different 

 periods of the growth of the plant. Wishing to 

 avoid entering upon debateable ground in noticing a 

 subject which remains intricate and obscure, not- 

 withstanding all the laborious treatises to which it 

 has given rise, the forms which the disorders assume, 

 and the bad effects by which they are followed will 

 be plainly but briefly described, leaving the question 

 of their classification to more professional hands. 



Three distinct and dissimilar causes are assigned 

 for the production of these disorders cold and 

 frosty winds sultry and pestilential vapours and 

 the propagation of a parasitical -fungus. The first 

 of these causes acts by stopping the current of the 

 juices; the leaves, being then deprived of a necessary 

 portion of nutriment, speedily wither and die, when 

 the juices, which are impeded in their passage, swell 

 and burst the vessels, becoming then the food of 

 myriads of little insects. These make their appear- 

 ance so suddenly as to have been considered the 

 cause rather than one of the effects of the disease. 

 The second cause of blight occurs after the grain 

 has attained its full growth. It has been observed 

 to happen mostly after heavy showers of rain, which, 

 occurring about noontide, have been succeeded by 

 clear sunshine. The plants are most commonly 

 attacked thus about the middle or end of July. Mr 

 Loudon informs us that ' in the summer of 1809, a 



