Ramaley : iivpocotyl and ei'ICOTyl in woody plants. 91 



The stele of the hypocotyl has two xylem bundles and two 

 aggregations of phloem bundles. In the epicotyl the youngest 

 material examined has a complete ring of phloem and about 

 eight xylem bundles. Cork formation in the former region 

 takes place deep in the cortex instead of in the outermost corti- 

 cal layer. 



In their final structure the two regions are practically alike. 



Celtis occidentalis. 



Structure of Hypocotyl. 



The epidermis is composed of thin-walled cells, small, square 

 in cross section. There is no hypoderma. The elements of 

 the cortex are large. There are about twenty layers of cells. 



The cells of the endodermis are much smaller than those of 

 the cortex and on this account the endodermis is readily distin- 

 guished until considerable secondary growth of vascular tis- 

 sue has taken place. 



Starch is found in the endodermal region from the first ; 

 toward the close of the season it is found not only in the pith, 

 phloem and cortex, but very abundantly distributed throughout 

 the xylem. Large isodiametric crystals, long known in the 

 stem of this species (Moeller [1882], p. 74), make their appear- 

 ance in the cortex some time before the close of the first season. 



The stele, which is cylindrical from the first, has originally 

 four x3-lem bundles and two crescentic masses of phloem. At 

 an early stage the xylem forms a closed ring, while it is not 

 till sometime afterward that the two areas of the phloem become 

 united. 



Two interrupted rings of sclerenchyma appear later in the 

 first season, one of these is in the cortex and consists of much 

 larger groups of cells than does the other which is in the outer 

 phloem. 



The pith is large-celled. A more or less definite perimedul- 

 lary zone of small cells is at length developed. 



Cork formation begins at a late period in the outermost cell 

 layer of the cortex. 



Structure of Epicotyl. 



The cells of the epidermis are at first nearly square in cross 

 section but at a later time are considerablv flattened. There 



