56 THE VEGETATIVE SHOOT 



ever, definite in growth, the main axis, after growing a longer or 

 shorter distance below, comes above ground, the continuation of 

 the rhizome within the soil being carried on by lateral branches 

 (2, Fig. 22). In perennial rhizomes of definite growth, such as 

 those of sedges, grasses, and many other plants, the permanent 

 part which remains below ground is a false main-axis or sym- 

 podium (p. 41). 



{b) The term sucker is applied to any adventitious shoot which 

 originates below ground on the stems or roots of shrubs and 

 trees. It possesses adventitious roots and by separation from 

 the parent may become a new individual plant. Suckers often 

 develop very rapidly and rob the parent of water and nutriment, 

 so that except for purposes of propagation they should be 

 destroyed. 



Ex. 31. — Examine the underground parts of couch-grass, bindweed, mint, 

 potato, horse-radish, asparagus, raspberry, and hop, and observe the scale- 

 leaves and the buds in the axils of some of them. 



Note the connection of the shoots which come above ground with the 

 underground parts. 



{c) A tuber is a shoot with a short, thick, fleshy stem, and 

 minute scaly leaves, in whose axils are buds or 'eyes.' The 

 most common tubers are developed below ground — e.g. those of 

 potato and Jerusalem artichoke — but they may occur on parts 

 of plants above the soil. The scaly leaves are not visible on 

 the fully-developed potato tuber, as they drop off or shrivel 

 up before ripening is accomplished. For the development and 

 structure of the potato tuber see pp. 457-462. 



{d) A corm is a short, thick, fleshy stem, with a few thin, scaly 

 leaves covering it, and bearing one or more buds at its apex. 

 Examples are seen in the ordinary crocus and gladiolus of 

 gardens. 



Fig. 23 is a section of a crocus in flower. At b is the solid, 

 fleshy stem of the corm, with the remains of an old corm {a) ad- 

 hering to it, and several adventitious roots {r). From its summit 



