40 THE USES OF PLANTS. 



at 8 to 15 per ton, in London (October, 1887). 

 The cake is a useful cattle food. In 1874, 145 million 

 pounds were exported from West Africa, mainly to 

 Marseilles, London, Hamburg, and Berlin.* 



4. ROOTS AND TUBERS. 



Of these more watery vegetables, the Potato 

 (Solanum tuberosum, L.) is the most important. Its 

 tropical substitutes, the Sweet Potato (Ipomcea Batatas^ 

 Lam.), and the Yams (Dioscorea\ and the Jerusalem 

 Artichoke (Helianthus tuberosus, L.), are somewhat 

 similar in composition ; the Turnip (Brassica cam- 

 pestriS) L., sub-sp. Rapa], Carrot (Daucus Carota, L.), 

 Parsnip (Pastinaca sativa, L.), Beetroot (Beta rubra, 

 B.C.), and Onions (Allium Cepa, L.), less so. 



The POTATO is the tuber, or underground enlarge- 

 ment of a branch of Solarium tuberosum, L., a native 

 of Chili, and apparently of Peru and Mexico. It 

 was brought to Ireland by Sir John Hawkins in 

 1565 ; and to England by Sir Francis Drake in 1585, 

 and a year later by Sir Walter Rawleigh ; and is 

 engraved in Gerard's ' Herbal/ published in 1597 ; 

 but did not become popular until late in the last 

 century. It is now only second in importance among 

 our vegetable foods to the cereals ; and, besides being 

 extensively cultivated, especially in Ireland and 

 Scotland, is imported in large quantities from France, 

 Portugal, etc. Since 1845 our potato crops have in 

 damp summers been devastated by a fungoid mildew 

 (Phytophthora infestans, De Bary). The potato con- 

 * ' Encyclopaedia Britannica,' vol. xi. 



