30 



MORPHOLOGY, OE COMPARATIVE ANATOMY. 



terminal bud. In some cases these tubers are rounded ; in others they 

 are divided below, so as to become palmate (tig. 22). The tubers of 

 Bunium (fig. 19) belong to the root. 



Rhizome. The rhizome or root-stock is a body composed of 

 an indefinite number of corm-like axes permanently connected 

 together, so as to form an elongated, root-like stem, more or less 

 clothed with leaf-scales (fig. 23). Its internodes are generally 

 little developed ; sometimes, however, regions with developed in- 

 ternodes alternate with others wherein they are undeveloped, 

 giving a nodose character ; when it has the internodes much de- 

 veloped (figs. 12 & 25), it approaches in character (through 

 "runners" &c.) to creeping leafy stems. Its texture and appear- 

 ance vary from herbaceous or fibrous (fig. 25) to tuberous (fig. 23) ; 

 its direction is usually horizontal, though in some cases it is vertical 

 (fig. 24) ; and in the majority of cases it grows under ground. 



Examples of the rhizome are very numerous among herbaceous peren- 

 nial plants, both Dicotyledons and Monocotyledons. The Iris affords 

 an example of a tuberous rhizome which may be understood by com- 

 paring it with a corm like that of Arum maculatum, and by supposing 

 that the older portions of this survive for many years, so as to form a 

 creeping, more or less branched mass. The Solomon's Seal (fig. 23), Sweet- 

 flag (Ac&rus), Ginger, Water-lily, &c. afford other well-known examples. 



Fig. 24. 



Fig. 23. 



Rhizome of Solomon's Seal (Convallaria polygonatum} : 

 a, bud for next year; 6, flowering stem of the present 

 year ; c & d, scars of the flowering stems of two pre- 

 ceding years. 



Vertical rhizome of Cicuta virosa, 

 cut through perpendicularly. 



In some of these (called definite rhizomes*) the flowers appear to be pro- 

 duced by terminal buds, which take an ascending direction and lose them- 

 selves in the inflorescence, the onward growth of the stem being effected 

 by means of axillary buds. In others (indefinite rhizomes} the growth 

 is continuous by the formation year after year of a terminal leaf-bud. 

 Rhizomes of more solid texture, but of analogous construction, occur in 

 many Ferns, as in Aspidium Filix-mas, also in most of the Rushes 



