72 THE STEM. 
interrupted from any cause, a circular arrangement is the consequence, —an 
arrangement so conspicuous in the organs of the flower (61, 2, 5, 2), and in the 
leaves of the Stellate, and other plants. 
-175. When a single leaf arises at a node the arrangement is 
more obviously spiral, and is said to be alternate. When two 
arise at each node they are placed opposite to each other, and at 
right angles to the adjacent pairs. 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 arrangement of the branches, when 
divested of all disturbing causes, is found to be spirat; that is, 
alternate in most plants, opposite in the ash, &c., or vertictllate 
in the pine, &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 modifications. It has 
already been stated, that although its tendency is at first upwards, it does not 
always arise above the surface. Hence the primary division of this organ into 
subterranean and aerial. 
177. The susTERRANEAN STEM was deemed 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. 
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