Ramaley : IIYPOCOTYL AND EPICOTYL IN WOODY PLANTS. 107 



In the hypocotyl there are at first 

 four pairs of xylem bundles and a 

 number of phloem bundles. Four 

 large groups of sclerenchyma soon 

 make their appearance in the peri- 

 cycle. In the epicotyl, on the 

 other hand, a closed ring of phloem 

 surrounds usually about six xylem 

 bundles. No differentiated peri- 

 medullary zone was distinguished 

 in the hypocotyl. 



The structure of the two regions 

 at the close of the first year differs 

 only in the perimedullary region and 

 pith ; the formation of cork having 

 removed the epidermis and hypo- 

 derma. 



Gleditsia 

 triacanthos 



FIG. 10. 



PAPILIONACE^E. 



Amorpha fruticosa. 



Structure of Hypocotyl. 



The epidermis consists of cells rather small, somewhat thick- 

 walled, square or nearly so, in cross section, at length becom- 

 ing flattened. The cells of the cortex are large ; those imme- 

 diately below the epidermis somewhat smaller, but not forming 

 a definite hypoderma. 



The endodermis of thin-walled cells containing starch re- 

 mains distinct for some time. Toward the close of the first year 

 its exact position cannot be determined, although it can be lo- 

 cated approximately. A small amount of starch is scattered 

 throughout the cortex, pith and pericycle as well as the endo- 

 dermis, even in the youngest stage. This is not the case in 

 most species. Later the phloem and the medullary rays also 

 come to be filled with starch. 



The stele is at first quadrangular, and remains so for a con- 

 siderable length of time. There are four conjoint vascular 

 bundles, and in addition there appear a few small patches of 

 phloem. The bundles soon tend to unite in pairs. Xylem and 

 phloem at length form complete zones. The medullary rays 

 are very numerous ; they are one cell in width. 



