Ramaley : HYPOCOTYL AND EPICOTYL IN WOODY PLANTS. 119 



The phloem, in the youngest material examined, forms a 

 complete ring. There are about six xylem bundles. These 

 soon fuse. 



Considerable masses of stereom develop at the periphery of 

 the phloem forming a broken sheath. 



The pith is large-celled. There is present a definite peri- 

 medullary zone of small cells containing starch. The cell walls 

 are lignified. 



Cork is produced in the outermost hypodermal layer as in 

 other species of Rhamnus (cf. Moeller [1882], pp. 292 et seq.). 



Comparison of Structure of Hypocotyl and Epicotyl. 



The hypocotyl has a thicker cortex than the epicotyl ; it does 

 not have a hypoderma ; epidermal hairs are absent ; the scleren- 

 chymatous ring found in the epicotyl is here absent. 



The endodermis of the hypocotyl remains distinct for a 

 greater time than that of the epicotyl. The former region has 

 originally four vascular bundles ; the latter has, in the youngest 

 material examined, a zone of phloem 

 and about six xylem bundles. Cork 

 formation in the hypocotyl is endoder- 

 mal while in the epicotyl it is hypoder- 

 mal. 



VITACE^E. 



Vitis cordifolia. 



Rhammw 



purehians 



Structure of Hypocotyl. 



The cells of the epidermis are nearly 

 square in cross section, but become at 

 length considerably flattened. Many 

 of them are somewhat prolonged, 

 forming short, blunt papillae. A thick 

 cuticle is present. In cross section it 

 appears minutely notched. 



Three or four of the outer layers 

 of the cortex are small-celled, but not collenchymatous. The 

 cells of deeper layers are larger and all about the same size. 



The endodermis is small-celled, and is for a long time read- 

 ily distinguished because it contains starch. Starch is gen- 

 erally absent from the other tissues, but, at a later time, ap- 

 pears in the pith. 



FIG. 17. 



