Ramalcy : IIYPOCOTYL AND EPICOTYL IN WOODY PLANTS. 127 



The stele is small ; in cross section it is circular. There are 

 at first six, seven or eight conjoint vascular bundles arranged in 

 a circle. Eight is probably the original number, but fusions 

 often take place between adjoining bundles. .Complete zones of 

 xylem and phloem are formed at an early stage. About this 

 time four small groups of sclerenchyma appear in the pericycle ; 

 they are equidistant. These eventually become somewhat 

 divided, and other cells of the pericycle become sclerotic, so 

 that a number of small groups of stereom are found in this area. 



The pith is small in amount. The cells are large, with thin, 

 slightly lignified walls. There is a perimedullary zone of small 

 cells containing starch. 



Cork formation takes place in the outermost layer of cortical 

 cells. 



Structure of Epicotyl. 



The epidermal cells at first are oblong in cross section ; 

 the long axis is at right angles to the periphery of the section. 

 Later the shape is more nearly square. There are many straight, 

 blunt epidermal hairs. 



The first two or three cell layers of the cortex are collenchy- 

 matous. The other layers are rather small-celled parenchyma. 



The endodermis, though at first distinct on account of the 

 presence of starch in its cells, was not recognized in older ma- 

 terial. Starch is absent from the other tissues in the early 

 stages, but is at length found in the cortex, phloem-, medullary 

 rays and perimedullary zone. 



Toward the end of the first year a narrow, much interrupted 

 ring of sclerenchyma appears at the outer edge of the phloem. 

 The cells are small with very narrow lumen. 



The number of vascular bundles is somewhat variable. 

 About twenty is the usual number. These soon unite to form 

 zones of xylem and phloem. 



The pith is large, the cells thin-walled parenchyma. There 

 is a perimedullary zone of small cells containing starch. 



Cork arises in the outermost hypodermal layer, as it does in 

 the stem of Catalpa catalpa (cf. Moeller [1882], p. 184). 



Comparison of Structure of Hypocotyl and Epicotyl. 



The epidermis of the hypocotyl has fewer and shorter hairs 

 than that of the epicotyl. The former region has no hypo- 



