Ranialcy : iiypocotyl and eimcotyl ix woody plants. 97 



become flat. The two or three hiyers of the cortex just below 

 the epidermis are small-celled. The deeper layers are very 

 large-celled. 



The endodermis is small-celled and easily distinguished in 

 young material, but is eventually displaced and is not distin- 

 guishable. In the young stages starch is entirely absent from 

 the hypocotyl, but later is found sparingly distributed through 

 the various parenchymatous tissues. 



The stele, which is originally quadrangular, has four vascu- 

 lar bundles arranged in pairs. By their continued growth 

 zones of xylem and phloem are produced. 



About the time that a complete ring of xylem has been formed 

 four masses of sclerenchyma appear in the pericyle. Even- 

 tually other groups of pericyclic cells also become sclerotic. 

 The phloem imrriediately under these groups is better developed 

 than at other places. 



The pith is slightly quadrangular. The cells are thin-walled. 

 A definite perimedullary zone was not distinguished. 



The cork cambium is produced in the outermost layer of cor- 

 tical cells. 



Structure of Epicotyl. 



The cells of the epidermis, when seen in cross section, ap- 

 pear square or tangentially elongated. A narrow collenchyma- 

 tous h3'poderma is developed. The remaining cells of the cor- 

 tex are all about the same size. 



The endodermis is distinct in young material, owing to the 

 presence of starch in its cells. At a later time starch is distrib- 

 uted in small amount in the various parenchymatous tissues. 



The number of primary xylem groups in the stele is about 

 six or eight. Groups of phloem are somewhat more numerous. 

 Closed zones of xylem and phloem are produced very early. 



The outer phloem has many groups of sclerench3'matous 

 fibers. These groups are close together, separated only by 

 medullary rays. A small amount of sclerenchyma is produced 

 in the cortex. 



The pith is rather large, and composed of cells with thin, un- 

 lignified walls. No perimedullary zone was distinguished. 



Cork is developed in the outermost cell layer of the cortex 

 (cf. Moeller [1882], p. 229). 



