FOODS, FOOD-STUFFS, AND FOOD-ADJUNCTS. 41 



tains 75 per cent, of water and 15 per cent, of starch. 

 This starch is but little affected by the disease. It 

 has been already mentioned as a substitute for arrow- 

 root and as a source of glucose. The latter substance 

 is obtained by boiling the starch with dilute sulphuric 

 acid ; and is largely used in brewing and in distilling, 

 yielding Potato spirit or British Brandy. From Potato- 

 starch also, by roasting, British gum, or Dextrin, used 

 for postage-stamps, etc., is also prepared. Whilst the 

 Potato belongs to the Nightshade Order (Solanace&\ 

 the Sweet Potato belongs to the Convolvulacea, and 

 the Yams to the Monocotyledonous Dioscoreacea. 



The SWEET POTATO (Ipomcza Batatas, Lam.), 

 unknown in a wild state, is extensively cultivated 

 throughout the tropics and in Southern Europe. It 

 is imported in small quantities from Spain. Its 

 tubers reach a far larger size than those of the Potato, 

 from which they differ also in containing 3 per cent, 

 of sugar. An allied species, Ipomcza chrysorhiza, 

 Hook, fil., is eaten under the name of Kumarah by 

 the Maoris of New Zealand. 



YAMS are the tubers of several species of Dioscorea 

 (D. sativa, L., and alata, L., natives of India, D. Batatas, 

 native of China, etc.), which sometimes reach a weight 

 of 30 or 40 lb., and resemble potatoes even more 

 closely than the Sweet Potato. D. Batatas, the 

 Chinese Yam, yields enormous crops in France and 

 Algeria, and is hardy here, but is not appreciated. 



JERUSALEM ARTICHOKES, the tubers of Helian- 

 thus tuberosus, L., a Composite plant, introduced from 

 the northern United States early in the seventeenth 

 century, but a native of Mexico or Brazil, take their 



