PRAIRIE OF ECONOMIC PLANTS. 337 



Ireland, wliere Potatoes had for years been almost tlie sole 

 article of food with the poorer class. Since that period, and on 

 account of this disease, the crop has been uncertain throughout 

 all countries. 



Besides the usual culinary purposes for which Potatoes are 

 used, a large quantity of starch is manufactured from them, 

 equal to arrowroot, and used for many domestic purposes. It 

 enters largely into the composition of wheaten bread, sometimes 

 even to excess. From the starch a gum is obtained called 

 Dextrine, which is used in the arts. The Potato yields by dis- 

 tillation a strong spirit, and by fermentation a wine is obtained; 

 the spirit in flavour resembles brandy. Consequent on the 

 disease of late years deteriorating the crops in this country, and 

 the supply falling short of the demand, large quantities are 

 imported, chiefly from France, the weeMy consumption of 

 London alone being equivalent to 500 tons. The quantity of 

 baked Potatoes sold by vendors in the streets is estimated at 60 

 tons weekly between September and April. The disease is 

 caused by a microscopic fungus called Peronospora infestans, 

 which rapidly spreads over the plant, whole fields becoming 

 black in a night ; its mycelium enters the tubers^ causing them 

 to soften and rot. Much has been written on this disease, and 

 rewards offered for its prevention or cure, but hitherto wuthout 

 any satisfactory result. 



Pottery Tree {Ifoquilea ictilis), a plant of the Cocoa Plum 

 family (Chrysobalanace^e), consisting of tall trees, natives of the 

 forests of Brazil and Guiana. Spruce describes them as straight, 

 slender trees, 100 feet in height. The bark is very hard and 

 brittle, and contains a great quantity of silica, which the 

 Indians obtain by burning the bai^k, and mixing the residue 

 with clay to form pottery- ware vessels to stand fire heat. In 

 Trinidad the bark of a species of Eirtella, S. silicea, a genus of 

 the same family, is used for similar purposes. Specimens of the 

 bark and of the vessels made from these pottery trees may be 

 seen in the Museum in Kew Gardens. 



Prairie Turnip {Psordea esculenfa), a tuberous-rooted herb 



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