PHYTOPATHOLOGY. 87 



as lies just before it, and so runs scudding along 

 betwixt the skin and the pulp of the leaf, leaving 

 a whitish streak behind it, where the skin is now 

 loose, as the measure of its voyage" a by no 

 means inadequate description of the injury and its 

 cause. 



During the eighteenth century several academic 

 treatises or dissertations dealing with diseases of 

 plants appeared. 



But as a rule we only find disjointed notes. 

 Hales (1727-33) discusses the rotting of wounds, 

 canker, and a few other matters, but much had to 

 be done with the microscope ere any substantial 

 progress could be made. 



With the nineteenth century, and the founding 

 of the modern theories of nutrition by Ingenhousz, 

 Priestley, and De Saussure, we find a new era 

 started. As the discoveries of the microscopists 

 continued to build up our knowledge of the 

 anatomy of plants and began to elucidate the 

 biology of the fungi and other cryptogams, while 

 the chemists and physiologists laid the foundations 

 of our modern science of plant life, it gradually 

 became possible to tabulate and classify plant 

 diseases, and discuss their symptoms and causes 

 in a more scientific manner. Even in 1833, 

 however, Turpin, and a far better observer, Unger, 

 regarded parasitic fungi as due to diseased out- 

 growths of chlorophj'll-corpuscles and parenchyma 

 cells, views shared by Meyen (1837) and Schleiden 

 (1846). We may pass over the various treatises 

 of Wiegmann (1839), Meyen (1841), Raspail 



