Ramaley : HYPOCOTYL AND EPICOTYL IN WOODY PLANTS. 



99 



tinct smaller-celled perimedullary zone. No cork is formed the 

 first year. 



Structure of Epicotyl* 



The cells of the epidermis, at first square in cross section, be- 

 come very much flattened and develop a thick cuticle like that 

 of the hypocotyl. A more or less definite collenchymatous hy- 

 poderma is developed. The cortex is composed of about six 

 cell layers. 



The endodermis is not easily distinguished even in youngest 

 stages. The pericycle has some cells which in cross section 

 appear empty, while the neighboring cells contain starch. 

 These empty cells at a later time either become filled with 

 starch or else are displaced so that they are not recognized. 



Starch is present in the cortex, medullary rays, endodermis, 

 pericycle and pith. 



There are originally from nine to fifteen vascular bundles. 

 These usually fuse to some extent so that there come to be only 

 about six or eight. These remain easily distinguishable, since 

 the primary medullary rays are very broad. The growth of 

 the cambium produces no true phloem elements opposite the me- 

 dullary rays, although there is some thin-walled parenchyma. 



A crescent-shaped area of stereom is finally formed at the 

 outer edge of each phloem bundle. 



The pith becomes rather small in extent. There is a perime- 

 dullary zone of two or three layers of 

 smaller cells. According to Flot 

 [1893] these form at a later time five 

 or six layers of sclerotic paren- 

 chyma. The formation of cork was 

 not observed. It does not take place 

 the first year. 



Comparison of Structure of Hypo- 

 cotyl and Epicotyl, 



The hypocotyl has a thicker cor- 

 tex than the epicotyl : it is without 

 a collenchymatous hypoderma. The 

 endodermis is much more distinct in 

 the former region and the peculiar dis- 

 tribution of starch in the pericycle is 

 more pronounced. FIG. 6. 



Menisperniuni 

 canadeiise 



