394 Prof. H. Marshall Ward. The Relations between 



investigating complex chains of cansation, and give rise to specula- 

 tions of the most superstitious description. 



The Diseases of Plants and their Classification, fyc. 



The diseases of plants have been classified in various ways, at 

 different times, and by different observers. Passing over the earlier 

 attempts,* based for the most part on errors which were natural at 



Fia. 1. A young coffee plant (reduced), the leaves of which are badly infected 

 with the Uredinous fungus Hemileia vastatrix. The paler spots are bright 

 orange-yellow, the centre gradually turns brown, and then black as the tissues 

 are destroyed ; the granular appearance on the younger spots is due to the 

 spores of the fungus. Such yellowing of the leaves is a common symptom of 

 such diseases. 



* An excellent account of the earlier writers appeared in the 1 Gardener's 

 Chronicle,' 1854, from the pen of the late Rev. M. J. Berkeley, F.R.S. 



