TAXONOMY 
343 
Stems and leaves further characterized by the presence of glandular 
hairs containing aromatic volatile oil. These hairs consist of a 
short one-celled stalk and a head (gland) of six or eight cells. Inflo- 
rescence a raceme or spike of verticillasters (double dichesial cymes) 
or, as in the Ground Ivy, a reduced verticillaster. Flowers typically 
Fig. 188 . — Mentha piperita — Flowering branch. (Sayre.) 
pentamerous, rarely tetramerous; sepals five, synsepalous, ribbed 
and forming a tubular regular or irregular bilabiate (Scull cap, etc.) 
calyx whose upper lip is bifid and lower trifid; corolla of five to four 
gamopetalous petals, hypogynous, frequently two-lipped, the upper 
lip bifid, the lower trifid; stamens four, didynamous, rarely one pair 
alone fertile and the other pair reduced in some cases almost or 
