Ramaley : HYPOCOTYL AND EPICOTYL IN WOODY PLANTS. 125 



About the time that this is apparent four small groups of 

 sclerenchyma make their appearance in the pericycle just out- 

 side the original xylem bundles. Each of these is composed of 

 only six to ten cells with extremely thick walls. Later numer- 

 ous isolated, lignified sclerenchymatous cells appear in the outer- 

 most layer of the cortex ; a few also are found in the phloem 

 area. 



The pith is large-celled and thin-walled. The formation of 

 a cambium layer in the small-celled perimedullary region begins 

 some time before the close of the year. This will be further 

 noticed in the description of the epicotyl. 



Cork formation takes place in the second cortical layer, *'. <?., 

 in the cell layer immediately below the sclerenchyma which is 

 thus eventually lost. 



Structure of Epicotyl. 



The epidermis has a well-marked cuticle which, in cross sec- 

 tion, appears minutely notched. The cells seen in cross sec- 

 tion are about square, but become tangentially elongated toward 

 the end of the season. There are occasional short epidermal 

 hairs. 



The cells of the outermost layer of the cortex are somewhat 

 smaller than those of deeper layers. These are considerably 

 flattened. Although at first of about even thickness through- 

 out, the cortex soon grows in thickness at four equidistant 

 points giving the epicotyl a quadrangular prismatic shape. 



The endodermis, which in young stages is distinct, at length 

 becomes indistinguishable owing to displacement and crowding 

 of the cells caused by growth in the lower layers. Starch, 

 though present in the endodermal region, is found only in very 

 small amount in the cortex and pith until the close of the sea- 

 son. Even then the cells are not closely packed with it. 



Even in the youngest stage examined, i. e., second stage of 

 our arbitrary division, the phloem and xylem form complete 

 rings. 



The outermost cortical layer toward the end of the season be- 

 comes largely sclerenchymatous, although here and there are 

 cells with but slightly thickened walls. Certain cells of the 

 pericycle, at first but slightly differentiated, form, at length, 

 groups of very thick- walled cells. 



The pith is composed of large cells with thin, unlignified 



