Ramaley : HYPOCOTYL AND EPICOTYL IN WOODY PLANTS. 129 



Structure of Epicotyl. 



The epidermal cells are rectangular in cross section. The 

 radial is the long diameter at first but eventually the two diame- 

 ters are nearly equal. Many of the cells are prolonged to 

 form pointed hairs which are about three times as long as the 

 ordinary cells of the epidermis. 



A narrow collenchymatous hypoderma is developed ; this 

 shades off gradually into the ordinary cortex, which is quite 

 extensive. 



The endodermis is rather large-celled, the cells resembling 

 those of the cortex but containing starch. The endodermis re- 

 mains distinct throughout the first year. Starch, which is at 

 first absent from the other tissues, becomes, at length, dis- 

 tributed through all the parenchymatous elements. 



The stele, originally elliptical in cross section, follows the 

 general shape of the epicotyl. Eventually the epicotyl be- 

 comes cylindrical as does also the stele. In the youngest ma- 

 terial examined, the phloem forms a complete zone surrounding 

 a ring of about six xylem bundles, which soon fuse to form a 

 closed ring. 



A few of the cells of the pericycle become sclerotic after a 

 time. These are generally isolated ; not aggregated in groups. 



The pith becomes quite small ; it is surrounded by a well- 

 developed small-celled perimedullary zone whose elements con- 

 tain starch. 



The cork, like that of the hypo- 

 cotyl, arises in the epidermis. 



Comparison of Structure of Hypo- 

 cotyl and Epicotyl. 



The hypocotyl differs from the epi- 

 cotyl in its shorter epidermal hairs, in 

 the absence of a true hypoderma and 

 in the much looser parenchyma of its 

 cortex. 



The structure of the stele is also 

 very different, the hypocotyl having 

 originally four phloem bundles and 

 four xylem bundles, while in the epi- 

 cotyl the phloem, even in the youngest 



Cephalanthus 

 occidentals 



FIG. 23. 



