RcDiialcy : hvi'OCOTvl and ki'icotyi. in wcodv plants, 123 



The stele is four-sided. The general shape of tiie hypocotyl 

 sometimes follows that of the stele (cf. Irmisch [1876]). There 

 are originally four narrow curved phloem bundles and the same 

 number of small xylem bundles. The phloem soon forms a 

 closed ring; the xylem bundles increase in size, leaving for a 

 time a cruciform pith ; but eventually the xylem also forms a 

 complete ring and the pith is cylindrical. 



Four small groups of sclerotic cells make their appearance 

 in the pericycle about the time that the phloem ring is first 

 formed. These groups eventually become somewhat broken 

 up and numerous groups of fibers appear in the phloem ar- 

 ranged in three or more interrupted circles. 



The pith is large-celled. It is small in amount even from the 

 first. No definite perimedullary zone was distinguished. 



Cork formation, according to Flot [1890], is cortical or peri- 

 cyclic. 



Struct lire of Eficotyl. 



The cells of the epidermis are at first more nearly square in 

 cross section than those of the hypocotyl. They at length be- 

 come very much elongated in a tangential direction. 



The cortex is large-celled ; the cells of the outer layer are 

 rather small. No hypoderma is differentiated. Numerous 

 lysigenous secretion sacs are present. 



The endodermis is thin-walled ; the cells are small and con- 

 tain starch. 



The stele is at first somewhat quadrangular and becomes at 

 length elliptical, in cross section. In the youngest material ex- 

 amined the phloem forms a closed ring. The number of xylem 

 bundles is somewhat variable ; these are so disposed that the pith 

 is generally at first somewhat cruciform. 



The pericycle becomes, at length, largely sclerenchymatous ; 

 numerous interrupted rings of bast fibers begin to appear but are 

 only slightly thickened the first year. 



The pith, at first cruciform, becomes somewhat quadrangular. 

 There is a perimedullary zone {fide Flot [1893]). An inter- 

 nal cambium produces a ring of phloem just out'^ide the pith: 

 This is mentioned by DeBary [1884]. A few sclerotic cells 

 were noted at the inner limit of the internal phloem. 



According to Flot [1890] cork formation is sub-epidermal. 



