374 Cooke and Schively on Observations on the 



olus, and have remains of cytoplasm. They are nearly filled 

 with compound starch grains. The central pith cells also 

 contain a little starch, but the outer pith cells, near the bun- 

 dles, are densely packed with starch deposits. 



Histology of the Mature Root. 



The root is very nearly circular in cross-section. There 

 is a single epidermal layer of cubical thin-walled cells. These 

 walls are thinner than those of the parenchyma cells within, 

 and have a brownish-yellow color in the fresh material. 

 They contain a brown dense elliptical nucleus lying against 

 the inner wall. These epidermal cells never have a flat 

 external surface in the fresh state. The external wall either 

 bulges outward or is depressed and curves inward. This 

 fact, together with the thinness of the walls, seems to indi- 

 cate an absorbent function in these cells. 



The parenchyma is of large round thick-walled cells, 

 densely filled with starch grains. These cells do not taper 

 longitudinally, but flatten against each other. There are 

 strong indications of pore connections through their common 

 cell walls, and also a very evident lamellation. A large 

 nucleus is frequently seen against the glistening yellow cell 

 Vi^all, while considerable protoplasm and a nucleolus are 

 usually evident. Starch grains are abundant and are mostly 

 single or double, the complex forms being rarely found in 

 the stem. Some show an irregular, semi-dissolved outline. 

 Occasional parenchyma cells show a clear matrix, in which 

 lie, in a parallel direction, numerous shining crimson needle- 

 crystals. They are slender spindle-shaped forms, with thick 

 centre and pointed ends, about one-third the length of the 

 cell. Such cells occur in groups of two or three and contain 

 no starch. 



There is a small central bundle, not sharply separated 

 from the cortex, as an endodermis is absent. Across it 

 passes a central band of wood, consisting of a few spiral 



