196 PLANT ORGANS OR PARTS OF PLANTS. 



four feet in height. It has a creeping rootstock, from 

 which it sends off long stolons, by which it is propagated, 

 for the most part. The stems are square, erect, purplish, 

 slightly pubescent, and many times branched above. 

 The corolla is light purple, four-lobed, typically bilabiate, 

 with four enclosed didynamous stamens. The calyx 

 is five-lobed, about 2 mm. in length, purplish, and 

 pubescent, with simple multicellular and glandular hairs. 

 The corolla is about twice the length of the calyx. 



The drug is made up for the most part of the leaves. 

 These range from 5 to 8 cm. in length and about 2 cm. in 

 width, borne on a petiole about i cm. long. They are 

 oval to ovate lanceolate in general outline, finely serrate, 

 minutely glandular, and sparsely provided with hairs. 



Histology. — A cross-section of the leaf shows a 

 delicate epidermal layer with a layer of palisade 

 cells, beneath the upper surface; the lower epidermal 

 layer is bordered by open parenchymatic cells, which 

 are richly pored. The oil glands are usually short- 

 pedicelled ; short glandular hairs are also present as well 

 as elongated simple multicellular hairs. The cross- 

 section of the midrib or large vein shows collenchymatic 

 parenchyma, open collateral fibro- vascular bundles, with 

 delicate vessels' and thin-walled wood fibres and a few 

 bast fibres.* 



Powder. — A medium fine powder, is dark green in 

 color, and shows the following characteristic elements: 

 Parenchyma, rich in chlorophyll, simple multicellular 

 hairs, oil glands, sometimes showing menthol crystals 

 within, glandular hairs, ducts, fibres, fragments of floral 

 tissues, collenchyma, and pollen grains. 

 < The parenchyma is usually thin-walled and filled with 

 chlorophyll grains ; at times it is richly pored ; the aver- 

 age diameter of the cells ranges from 60 to 80 microns. 



The hairs are striking; they are thin-walled, usually 



* See Tschirch's angewandte Pflanzenanatomie, p. 120, Fig. 124. 



