THE DISEASES OF PLANTS. 61 



and that their presence even is often inisuspected, as in the 

 case of the potato rot, the cause of which was everywhere 

 sought in vain for manj' years, until at hist Mr. Berkeley, the 

 celebrated botanist of the Royal Horticultural Society in Lon- 

 don, demonstrated that a microscopic fungus was the undouljted 

 source of the terrible evil. "Where the carcass is, there the 

 eaoies are gathered together," and it has been discovered that 

 the potato plant, weakened by the assault of its principal 

 enemy, is subsequently attacked by no less than ten different 

 fungi. More than thirty species are parasitic upon the grasses, 

 which are infested by them, wherever cultivated, the sorghum 

 and cane of the tropics, as well as the oats and barley of the 

 North. The coffee-tree, the orange, the olive, and the mul- 

 berry suffer under the attacks of various blights, which, 

 obstructing the cells and stomata of the foliage, induce disease 

 and the failure of the looked-for crop. Even the silkworm 

 has become the victim of a fungus, to eradicate which millions 

 of dollars have been sent to Japan and China for the purchase 

 of health}^ ^ggs? which arc annually imported into Southern 

 Europe. Thus the knowledge of the origin of the disease has 

 led to the finding of a remedy, without which one of the great 

 industries of France and Italy must have perished. Still more 

 impressive is the fact that epidemic and contagious diseases 

 among men and animals are usually accompanied by the growth 

 of microscopic fungi on or within the bodies diseased, which 

 are often the cause of great discomfort, and sometimes of death. 

 The argument in favor of botanical studies might be still 

 further strengthened by allusion to the useful qualities of some 

 of the larger species of fungus. The chemical composition of 

 these remarkable plants is very peculiar, and resembles that 

 of animal fibre. Though the majority of them are exceedingly 

 poisonous, yet more than one hundred species are used for 

 food. The savages of Tierra del Fuego and New Zealand rely 

 upon them as staple articles of diet, and in all parts of Europe 

 they are regarded as delicious luxuries. In London, dried 

 trufiles are worth five dollars per pound, and other edible fungi 

 are sold at high prices ; and the demand generally exceeds the 

 supply. In Paris, also, immense sums are expended for them, 

 and, in 1867, there was one cultivator of common mushrooms 

 who had twenty-one fniles of beds, twenty inches in width, 



