262 THE SEED PLANTS : FORMS AND LIFE HISTORIES 



and becomes an independent plant. These offsets 

 are regularly used by gardeners to propagate the 

 plant. ' 



Some horizontal rhizomes, on the other hand, are 

 thick, fleshy and comparatively slow growing (Solomon's 

 Seal), and these store considerable quantities of organic 

 food reserves during the winter. 



Tubers. — When the food is localised in a definite 

 portion of an underground stem, the rest being thin, 

 the swollen portion is called a tuber (Fig. 41, C, t). 

 The beginnings of tuber formation are well seen in the 

 Chinese Artichoke {Stachys tuberifera). Many species of 

 Stachys have uniform rhizomes, but in the Chinese 

 Artichoke several successive internodes are swollen, 

 the nodes being somewhat constricted by comparison 

 with the internodes and bearing alternating pairs of 

 triangular scales. A thinner portion of the rhizome 

 follows, the terminal bud turning up to produce the 

 aerial shoot. The lateral buds which continue the 

 growth and branching of the rhizome grow out to form 

 several thin internodes, followed by the thick tuberous 

 portion in each case, so that the tubers are connected 

 together in branching chains. 



In the Potato plant (Solanum tuberosum) the main 

 shoot is erect, but thin lateral shoots are formed 

 from buds in the axils of basal leaves, and each of these 

 grows horizontally or obhquely downwards and swells 

 at its apex into a potato tuber. When very young 

 (about the size of a pea) the tuber is seen to bear minute 

 scale leaves, but these do not grow as the body of the 

 tuber swells, and when the latter is full grown their 

 scars appear, with the bud in the axil of each, as the 

 " eyes " of the potato. The " rose " end of the potato 

 is the apex of the tuber where the " eyes " are crowded. 



