RamaJcy : HYPOCOTYL AND EPICOTYL IN WOODY PLANTS. 103 



bundles and eight paired xylem bundles. Eventually closed 

 rings of xylem and phloem are formed. 



At the corners of the stele in the pericycle groups of scleren- 

 chyma are formed. The cells become very thick-walled and 

 each group quite large. 



The pith is large. The cells are rather thick-walled. No 

 definite perimedullary zone was distinguished. 



In the material examined cork formation had not commenced. 



Structure of EpicotyL 



The epidermal cells are thin-walled, square in cross section, 

 becoming at length much flattened. There is no collenchyma. 

 The cortex is narrow ; the cells are about the same size as those 

 of the epidermis. 



The endodermis is composed of thin-walled cells. After 

 secondary growth of the stelar tissues it cannot be definitely 

 seen. The cells are about the same size as those of the cortex ; 

 they contain starch. Starch is found at a later time in the 

 various parenchymatous tissues. 



The number of vascular bundles is variable. Usually there 

 are about twelve. These, at length, fuse to form closed rings 

 of phloem and xylem. 



The pericycle develops a sheath of sclerenchyma which almost 

 completely shuts in the phloem. The cells were not very thick- 

 walled in the material examined. 



The pith is large, the cells rather 

 thin-walled. A perimedullary zone 

 of small-celled parenchyma at length 

 becomes differentiated. 



No material old enough to show 

 cork formation was examined. 



Comparison of Structure of Hypo- 

 cotyl and EpicotyL 



The hypocotyl differs from the epi- 

 cotyl in having a thicker cortex with 

 a narrow small-celled parenchyma- 

 tous sheath. The cells of the cortex 

 are also larger. 



In its primary stelar structure the 

 differences are very marked. The 



1'nrkiiiMMiia 

 aculenta 



FIG. 8. 



