62 Stevens — Science of Plant Pathology. [June 



tury. Fungi had been seen upon the plant and had been 

 described in some detail during- the preceding decade, but 

 instead of being recognized as casual agents of disease they 

 were, as was the fate of bacteria in the case of animal dis- 

 eases, by many regarded as products of disease. Before the 

 study of plant diseases could be scientifically undertaken, the 

 basic facts of plant nutrition were to be discovered, the para- 

 sitic habit of the fungi proved, the minute anatomy of the 

 plant disclosed. Epoch-making in the disclosure of these des- 

 iderata, which may be said to have given birth to plant 

 pathology as a science in the second decade of the nineteenth 

 century were the investigations of the early Dutch, French, 

 German and English botanists. Like bacteriology, plant 

 pathology is an infant science of the last century, owing its 

 being to the perfection of the microscope. 



In the last two decades of the last century, scientific effort 

 concerned itself chiefly with accumulating knowledge con- 

 cerning fungi and insects. Vast numbers of these were clas- 

 sified, catalogued and described. In other words, the means 

 of diagnosis were perfected and diseases were grouped into 

 natural classes according to their casual agents. Attempts 

 toward the development of methods of treatment by the use 

 of various sprays were more or less effective. Indeed, spray- 

 ing had been advocated to some slight extent for a century or 

 more as a remedy for insect and other plant diseases. The 

 varietj' of spra} r ing substances ranged from clay, ashes and 

 cow manure to sulphur, lime, salt, etc. One writer recom- 

 mended "The applying around the base of the tree; flax, rub- 

 bish, sea weed, ashes, lime, sea shells, sea sand, mortar, clay, 

 tanner's bark, leather scraps, etc." — evidently not a homeo- 

 pathic prescription. The variety of substances recommended 

 raises suspicion that the efficiency of no formula was demon- 

 strated. In 1787 we find the heroic advice, 'just wet the trees 

 infested with lice, then rub flowers of sulphur upon the 

 insects, and it will cause them all to burst.' Some decided 

 progress was, however, made. As early as 1842, a whale 



