104 MINNESOTA BOTANICAL STUDIES. 



hypocotyl has four phloem bundles and eight xylem bundles 

 instead of a large number of conjoint bundles. It has four 

 large groups of stereom instead of a narrow, almost continuous 

 sclerenchymatous sheath. 



Cercis canadensis. 



Structure of Hypocotyl. 



The epidermal cells are rectangular in cross section ; the 

 radial diameter is the longer. These cells never become tan- 

 gentially elongated. The cells of the outer cortex are smaller 

 than those within. An indefinite sheath of small-celled paren- 

 chyma similar to that in Parkinsonia can sometimes be recog- 

 nized. 



The endodermis is small-celled ; it remains distinct through 

 the first year. Its cells contain starch. Starch is also present 

 toward the close of the year in the pith. 



The stele is originally quadrangular. There are four xylem 

 bundles and four phloem bundles. These, at length, develop 

 into closed rings. 



Four small groups of sclerenchyma make their appearance 

 in the pericycle at an early time and become, at length, consid- 

 erably extended. 



The pith finally becomes cylindrical. The cells are large 

 and thin-walled. The perimedullary zone is not clearly dif- 

 ferentiated. 



Cork formation takes place in the cortex either next to or 

 very near the endodermis. It begins sometime before the close 

 of the season. 



Structure of Epicotyl. 



The epicotyl is somewhat quadrangular in the early stages. 

 The epidermal cells are rectangular in cross section. The 

 tangential diameter is the greater. There is no hypoderma. 

 The cortex is thin. The cells are all about the same size. 



The endodermis was not definitely distinguished. In the 

 youngest material examined the phloem forms a closed ring. 

 There are four large primary xylem bundles. There are also 

 some smaller ones. The latter have often only one or two 

 xylem cells. A closed zone of xylem is soon produced. 



Nearly all the cells of the pericycle become, at length, scler- 

 otic, thus forming an almost continuous sheath with but few 

 parenchymatous cells. 



