THE MICROSCOPE. 185 



cally are nearly round. The prosenchymatous cells present no 

 features requiring description. 



The starch of Apocynum cannabinum, as previously stated, is 

 found in the cells of the inner bark. The granules are exceedingly 

 irregular, both in size and shape; they are in fact sufficiently so to 

 make this feature somewhat characteristic. Several successive 

 measurements of twenty grains, taken so as to include, as nearly as 

 possible, all in a given space, gave an average long diameter of 

 .0082 raillimeter and .0074 millimeter short diameter. The extremes, 

 so far as measured, were .014 millimeters maximum, and .0025 milli- 

 meter minimum. In shape, the more perfect granules are nearly 

 oval, others approach angularity, or are variously contorted, while 

 the smaller grains are nearly round. 



In the center of the woody column are a few nearly spherical 

 pith cells. Bast cells, although a prominent feature in the bark of 

 the stem, were not observed in any of the specimens examined. 



Apocynum androssemifolium has a long, running root. When 

 dry it is contorted, frequently having the woody remains of its stalks 

 attached. It is shriveled longitudinally, and often marked by trans- 

 verse fractures, that, extended through the bark and scales ofiF 

 The root breaks with difficulty, its central part being woody. Ex- 

 ternally, the bark is dark brown, white upon its inner surface, and 

 readily separates from the central or ligneous part of the root; it 

 is very bitter. The central part of the root is smooth and firm, bends 

 before breaking, and usually requires considerable twisting before 

 the woody fibers give way. Attached to the root are rootlets, not 

 very plentiful, which bear a general resemblance to the main root, 

 their central portion being woody, and covered by a brown epidermis. 

 The root of Apocynum androssemifolium presents the following 

 histological characters: First, an outer layer of cork, usually from 

 three to six cells in thickness; next, a zone of cortical tissue made 

 up of irregularly shaped cells containing starch, this tissue occupying 

 generally about one-eighth the distance from cortex to center of the 

 stem. The inner portion of this zone contains many bast cells, the 

 walls of which are strongly thickened; they are arranged in groups, 

 are quite regular in size and form when examined in transverse 

 section, and from this view show, like starch grains, a cross under, 

 polarized light. The successive layers of their walls, also, show as 

 well marked striiB. Numerous intercellular spaces are seen in this 



