AXIS AND APPENDAGES. Ill 



alogy to animal metamerism, though not usually recognized 

 or designated by the same term. All of these conditions of 

 differentiation and symmetry are more easily made out by an 

 examination of the aerial portion. 



The plant as a whole, may be regarded as consisting of 

 an axis (the rhizome and its branches) which bears a number 

 of appendages in the form of roots and leaves. The axis forms 

 the central body or trunk of the plant, and in it most of its mat- 

 ter and energy are stored ; the appendages are organs for taking 

 in food, for excretion, for respiration, for reproduction, etc. 



The Underground Stem, or Rhizome, and its Branches. The 

 rhizome is a hard black, elongated, and branching stem, gener- 

 ally flattened somewhat in the vertical direction as it lies in the 

 earth, and expanded slightly on either side to form well-marked 

 lateral folds the lateral ridges. Its thickness is seldom more 

 than half an inch, and usually considerably less. In transverse 

 section it has the outline shown in Fig. 48, and the marginal 

 part only is black. The branches repeat in all respects the form 

 and structure of the main axis. Both the main axis and the 

 branches end either in conical, pointed, and fleshy structures 

 about two inches long, or in blunt, yellowish knobs, plainly de- 

 pressed in the centre. At these ends the rhizome grows ; hence 

 they are called the growing points or apical buds (Figs. 44, 47). 



Besides the apical buds the rhizome bears nearly always one 

 or more dead, decaying tips. These arise in the following man- 

 ner : After attaining a certain length both the rhizome and its 

 branches gradually die away behind. Death of the hinder part 

 follows at about the same rate with which growth advances at 

 the apical buds ; so that the total length may not change mate- 

 rially from year to year. It is obvious that this process must 

 result in the gradual and successive detachment of the branches 

 from the main axis. Each branch, now become an independ- 

 ent rhizome, repeats the process; and in this manner a single 

 original rhizome may give rise to large numbers of distinct 

 plants, all of which have been at some time in material connec- 

 tion with an ancestral stock. This process is evidently a kind of 

 reproduction (though it is not the most important or most obvi- 

 ous means for the propagation of the plant), and in this way a 

 large area may be occupied by distinct, though related, plants 



