192 PHARMACEUTICAL BOTANY 
tive layer of cork is developed beneath the abscission layer either 
before or after the fall of the leaf which seals the wound and forms 
the leaf scar. The shape of many of the leaf scars are diagnostic 
for the stems bearing them. 
UNDERGROUND OR SUBTERRANEAN STEMS.—A RHIZOME is a 
creeping underground stem, more or less scaly, sending off roots 
from its lower surface and stems or leaves from its upper. The 
rhizome grows horizontally, vertically or obliquely, bearing a 
Nit WI 
Fic. 122.—Rhizome of Solomon’s Seal (Polygonatum biflorum). 1, scar of last 
year’s overground stem; 2, base of this years aerial stem; 3, terminal bud of next 
year’s aerial stem. sc, scale leaves; s, scars (annulations) of old scales; r, rootlets. 
5¢ natural size. (Gager, after Gapp.) 
terminal bud at its tip. Its upper surface is marked with the 
scars of the bases of aerial stems or leaves of previous years. 
Examples: Triticum, Rhubarb, etc. 
The Tuser is a short and excessively thickened underground 
stem, borne usually at the end of a slender, creeping branch, and 
having numerous “eyes” or axillary buds. Examples: Tubers of 
the Potato and Jerusalem Artichoke. 
The Cor is an underground stem excessively thickened and 
solid and characterized by the production of buds from the center 
of the upper surface and rootlets from the lower surface. Exam- 
ples: Colchicum, Jack-in-the-Pulpit, Crocus, etc. (See Fig. 127.) 
A BuLB is a very short underground stem invested by fleshy 
scales which represent storage leaves. It produces rootlets from 
its lower face and leaves and flower from its upper. 
Tunicated -bulbs are completely covered by broad scales which 
form concentric coatings. Examples: Onion, Squill, Daffodil. 
Scaly bulbs have narrow imbricated scales, the outer ones not 
enclosing the inner. Example: Lily. (See Fig. 127.) 
