4 BULLETIN 1021, U. S. DEPARTMENT OF AGRICULTURE. 



not fit under different conditions. It is well known that the length 

 of vine of any variety is greater in the South than in the North. The 

 length and size of the vine, as well as the size of the leaf, are greater 

 on heavy soils than on light sandy soils. In the description of the 

 Nancy Hall variety the stem is classed as short (under 4 feet long), 

 while in practically every region where this variety is grown to any 

 great extent the stem grows to be more than 4 feet in length. In the 

 vicinity of Washington, D. C, on a sandy-loam soil the stems grow 

 4 to 8 feet long. The vine of the Shanghai variety is also classed as 

 short, but under the conditions mentioned in connection with the 

 Nancy Hall it grows to be 6 to 9 feet in length. The stems of the 

 Ticotea and Florida varieties are also classed as short, while under 

 fairly favorable conditions they grow to a length of 6 to 9 or 10 feet. 



The other characters used in the key, with the possible exception 

 of the "Arrangement of hair on the upper surface of the leaf, if any," 

 and " Distinctness of wood elements in the root," are very important 

 and reliable. All characters should be considered in connection with 

 the mature plant, as many do not develop on new growth and some 

 disappear as the plant nears maturity. The shape of the leaves on 

 new growth is often very different from the shape of fully developed 

 leaves. The surface of young leaves may be covered with hairs, while 

 older leaves may be entirely smooth. The use of letters and numbers 

 rather than the terms for which they stand makes the key rather 

 awkward. 



Another attempt at classification of sweet-potato varieties is given 

 in Bulletin 33, " Estacion Experimental Agronomica," Santiago de 

 las Yegas, Cuba, entitled " Las Variedades Cubanas de Boniato." 

 This work deals to a certain degree with American varieties, much of 

 the material having been obtained in this country. In this system 

 of classification four groups — white, yellow, purple, and reddish — 

 are made, and these are further divided according to the color of the 

 stems, leaves, and veins on the leaves. This system of classification 

 is not sound, as the color of the roots varies greatly with difference 

 in soil and climatic conditions. 



PROPOSED SYSTEM OF CLASSIFICATION. 



The work on which the proposed system of classification is based 

 was begun by the Bureau of Plant Industry in 1901 and has been 

 continued up to the present time. During the season of 1901 the 

 varietal work was carried on at College Park, Md., in cooperation 

 with the Maryland Agricultural Experiment Station. At the end of 

 the season, the work and the varietal collection were transferred to 

 the Bureau of Plant Industry. From 1902 to 1920 the collection has 

 been grown every year on the Potomac Flats, near Washington. The 



