APOCYNUM 541 



plants of this family. These tubes are very early developed, being 

 present even in the embryo. They occur in the pith, are distributed 

 throughout the tissues of the bark, and are associated with the vas- 

 cular bundles in the veins of the leaf. They usually have thin walls, 

 narrow lumina, and the contents may be a caoutchouc-like substance, 

 so that on the fracture of the bark it may be drawn out into thin 

 threads as in the Celastracese. The latex may also contain starch 

 grains and distinct nuclei. Secretory cells are also present in the 

 barks of some of the genera, as Aspidosperma. Bast fibers occur in 

 the pericycle, either singly, or in groups. The walls of the tracheae 

 are usually marked with simple pores, except when in contact with the 

 medullary rays, when the dividing wall possesses bordered pores. 

 The wood fibers have either simple pores or bordered pores. The 

 medullary rays are narrow. Strands of intraxylary phloem occur 

 in the pith. Calcium oxalate is secreted in the form of solitary 

 crystals, styloids or rosette aggregates. The non-glandular hairs 

 are either unicellular or uniseriate. Glandular hairs are wanting, 

 except in the leaves of the oleander, in which the hairs consist of 

 several rows of elongated cells, which are covered with a palisade-like 

 secretory epidermis. In the oleander the stomata are situated in 

 deep pits, which are covered with long hairs. In the leaves of Aspi- 

 dosperma the palisade cells are often more or less lignified. In the 

 leaves of Strophanthus the subsidiary cells of the stomata are parallel 

 to the pores. 



APOCYNUM. Canadian Hemp. The dried root of Apocynum 

 cannabinum (Fam. Apocynacese), a perennial herb growing in fields 

 and thickets in the United States and southern Canada (Fig. 231). 



Description. Cylindrical, somewhat branched, usually broken 

 into pieces 4 to 10 cm. in length, 5 to 10 mm. in diameter; externally 

 light brown, longitudinally wrinkled and transversely fissured, with 

 few rootlets or rootlet-scars; fracture short; internally, bark light 

 brown, 1 mm. in thickness, easily separable from the lemon-yellow, 

 porous, slightly radiate wood; odor slight; taste of bark bitter and 

 acrid, of wood slightly bitter. 



Stem fragments are distinguished by having a comparatively 

 thin, finely fibrous bark and a hollow center. 



INNER STRUCTURE. See Fig. 232. 



Powder. Light brown or dark brown; starch grains numerous, 

 from 0.003 to 0.015 mm. in diameter, spheroidal, ellipsoidal, ovoid, 

 pyriform or more or less irregular, and with a hyaline central cleft 

 sometimes more or less altered, swollen; numerous fragments of 

 strongly lignified wood fibers, associated with tracheae mostly having 



