72 



THE STEM. 



interrupted from any cause, a circular aiTangement is the consequence, — an 

 arrangement so conspicuous in the organs of the flower (61, a, 6, c), and in the 

 leaves of the Stellatae, and other plants. 



175. When a single leaf arises at a node the arrangement is 

 more obviously spii-al, and is said to be alternate. When tivo 

 arise at each node they are placed opposite to each other, and at 

 right angles to the adjacent pahs. When three or more arise at 

 each node they are disposed, of course, in a circle, and are said 

 to be verticillate, or whorled. 



176. In like manner, the an-angement of the branches, when 

 divested of all disturbing causes, is found to be spiral ; that is, 

 alternate in most plants, opposite in the ash, &c., or verticillate 

 in the pme, &c. 



FIG. 22. — 1, Buds, terminal and lateral, with their scaly envelopes ; 2, the scaly bulb of 

 the lily, showing its analogy to the bud ; 3, vertical section of the same. 



a. The ascending axis is exceedingly various in form, size, position, and struc- 

 ture, existing in every plant under some one or other of its modiiications. It has 

 abready been stated, that although its tendency is at fii-st up^vards, it does not 

 always arise above the smfacc. Hence the primary division of this organ into 

 subterranean and aciial. 



177. The SUBTERRANEAN STEM was dccmcd a root by the ear- 

 lier botanists, and those plants which possessed such stems only 

 were called acaulescent or stemless, terms still in use, denoting 

 merely the absence of aerial stems. The principal modifica- 

 tions are the bulb, corm, tuber, rhizoma, and creeper. 



