ASPIDIUM. 121 



average 5 cm. in length, 0.5-1 cm. in diameter, slightly 

 curved, shining dark-brown. These are closely inter- 

 mingled with numerous light-brown chaffy scales and 

 numerous delicate branched roots. Internally the rhi- 

 zome is pale-green when fresh, yellowish and spongy 

 when old. Fragments of the stipes are good when green 

 only. The green character of the internal structure of 

 both rhizome and stipes is essential. This is usually 

 retained for from a half to two years after gathering, 

 at the end of which time the drug is of no value, and, in 

 fact, has suffered a gradual deterioration throughout the 

 whole period. 



Histology. — A cross-section of the rhizome shows an 

 angularly irregular outline; without is a layer, six to 

 eight rows deep, of brownish-yellow thick- walled polyg- 

 onal cells. In the light green thin-walled parenchymatic 

 ground tissue cells are numerous small, round or 

 oval starch grains, single or in groups of two or three. 

 Of frequent occurrence are round intercellular spaces into 

 which project one or more round stalked glands contain- 

 ing the dark green oleoresin. About midway between 

 the centre and periphery of the section is a single circle 

 of six to twelve (D. marginalis has five to seven) oval or 

 reniform concentric fibro-vascular bundles arranged with 

 the larger diameters at right angles to the radii. Each 

 of these is surrounded by an endoderm of thickened cells, 

 within which is the phloem tissue of the bundle and the 

 central xylem. The xylem is composed mostly of large, 

 angular, pitted, thick-walled tracheids, with here and 

 there, single or in groups of two, narrow pitted and scalari- 

 form ducts, imbedded in starch containing parenchyma. 

 In the outer phloem portion of the bundle three zones of 

 tissue may be distinguished. Within lie one or more 

 rows of parenchyma enmeshing the wide, thin- walled 

 sieve bundles. Surrounding these are several rows of 

 narrow, thick- walled, longitudinally elongated paren- 



