FORMS OF STEMS. 47 



which remains in some plants after the leaves, branches, and flower- 

 stalks have withered. In this ease the internodes are very short, and 

 the nodes are crowded together, so that the plant appears to be stem- 

 less. It is seen in perennial 

 plants, the leaves of which die 

 'down to the ground annually. 

 A Rhizome or root-stock (fig. 

 107) is a stem which runs 

 along the surface of the 

 ground, being partially cover- 

 ed by the soil, sending out 

 roots from, its lower side and 

 leaf-buds from its upper. It 

 occurs in Ferns, Iris, Hedy- rig. lor. 



chium, Aoorus or Sweet Flag, 



Ginger, Water-lily, many species of Oarex, Eushes, Anemone, Lath- 

 rsea, etc. By many the term rhizome is applied to stems creeping 

 horizontally, whether they are altogether or only partially subterranean. 

 The short underground stem of Arum maculatum differs from the 

 rhizome of Solomon's Seal, in the presence of the old axes in the latter, 

 and their decay in the former. A rhizome may then be considered as 

 a series of corms united together, the internodes or individual axes 

 being more or less elongated, and usually covered with leaf scales. In 

 rhizomes, called definite, the terminal bud gives off flowers, and the 

 lateral buds form the stem ; while in indefinite rhizomes the terminal 

 leaf-bud is formed annually. A rhizome sometimes assumes an erect form 

 as in Scabiosa succisa, in which the so-called prcemorse (proemorms, 

 bitten at the end) root is In reality a rhizome, with the lower end 

 decaying. The erect rhizome of Cicuta virosa shows hollow internodes, 

 separated by partitions. A Pseudo-bulb is an enlarged bulbous-like 

 aerial stem, common in Orchidaceous plants. It is succulent, often 

 contains numerous spiral cells and vessels, and is covered with a 

 thick epidermis. In the Kohl-rabi a peculiar thickened turnip-like 

 stem is met with. A Soboles is a creeping underground stem, 

 sending roots from one part and leaf-buds from another, as in couch 

 grass, Oarex arenaria, and Scirpus lacustris (fig. 108). It is often 

 called a creeping root, but is really a rhizome with narrow elongated 

 internodes. A Tuber is a thickened stem or branch produced by 

 the approximation of the nodes and the swelling of the internodes, 

 as in the potato (fig. 109 t). The eyes of the potato are leaf-buds. 

 Tubers are sometimes aerial, occupying the place of branches. 



Fig. 107. Portion of Bhizome, r, of Polygonatum multiflomm, Solomons Seal, forming 

 buds and adventitious roots, a, A bud in the progress of development, t, A bud developed 

 as a branch at the extremity of the,rhizome. cc. Cicatrices or scars, indicating the situa- 

 tion of old branches which have decayed. 



