Description and Classification 23 



produce the tubers (potatoes), which are the common 

 vegetable food. The nature of these tubers is further 

 rendered evident by the presence of "eyes" or leaf- 

 buds, which in due time lengthen into shoots and form 

 the haulm or stems of the plant. Such buds are not, 

 under ordinary circumstances, formed on roots. This 

 budding of the tubers furnishes an eflBcient method 

 of propagation, independent of seed production. Starch 

 and other matters are stored up in the tubers, as in the 

 seed, and are rendered available for the nutrition of the 

 young shoots. When grown under natural circumstances, 

 the tubers are relatively small, and close to the surface 

 of the soil, or even lie upon it. In the latter case, they 

 become green and have an acrid taste, which renders them 

 unpalatable to human beings, and as poisonous qualities 

 are produced similar to those of many Solanacese, they 

 are unwholesome. Hence the recommendation to keep 

 the tubers in cellars or pits not exposed to the light. 

 Among the 900 species of Solanum, less than a dozen 

 have this property of forming tubers. The production 

 of small green tubers on the haulm, in the axils of the 

 leaves of the potato, is not very infrequent, and affords 

 an interesting proof of the true morphological nature of 

 the underground shoots and tubers. This phenomenon 

 follows injury to the phloem in the lower parts of the 

 stem, preventing the downward flow of the elaborated 

 sap. 



CLASSIFICATION OF VARIETIES. PLATE II 



For the sake of convenience, the many varieties which 

 are now on the market may be classified. No one classi- 

 fication, however, will be adequate to cover all conditions. 

 Varieties differ somewhat from one part of the country 



