Ramaley : iiypocotyl and epicotvl ix woody plants. 109 



Comparison of Striicliirc of Hypocotyl and Epicotyl. 



In very young plants the hypocotyl shows a few slightly dif- 

 ferentiated layers of smaller cells in the outer cortex. The 

 €picotyl has nothing of the kind. 



The endodermis of the hypocotyl 

 is distinct in the early stages, but was 

 not definitely located in the epicotyl. 

 Starch appears earlier in the hypocotyl 

 and the four large groups of stereom 

 are not represented at all in the epi- 

 cotyl which, however, has an inter- 

 rupted circle of the same material. 



In the former region the stele is at 

 first quadrangular, while always cylin- 

 drical in the latter. Cork formation 

 in the hypocotyl is pericyclic, but is 

 cortical in the epicot}^. 



The final structure of the two regions 

 is very similar, save in the arrange- 

 ment of sclerenchyma. Fig. n. 



rViiiorpha 



fruticoBa 



Robinia pseudacacia. 

 Striccttire of Hypocotyl. 



The epidermal cells are oblong in cross section, radially 

 elongated at first, later becoming elongated in the tangential 

 direction. A few straight multicellular hairs are present. 

 There is no differentiated hypoderma. The cells of the cortex 

 are all about the same size. 



The endodermis is small-celled and contains starch. It is not 

 easily distinguished in material taken at the close of the grow- 

 ing season. Starch is also found in some of the pericyclic cells 

 in early stages. Later nearly all the parenchymatous tissues 

 have starch. 



The stele is originally quadrangular. There are eight phloem 

 bundles and four xylem bundles. These soon produce closed 

 zones. 



In the pericycle opposite each of the original xylem bundles 

 a group of stereom appears. These groups, at length, become 

 quite large. In addition to these, at the close of the first year, 

 there are some small patches of stereom irregularly disposed 

 just outside the phloem. 



