Ramaley : HYPOCOTVL AND EPICOTVL IN WOODY PLANTS. 121 



The pith of the hypocotyl becomes, at length, nearly ob- 

 literated. 



EL^EAGNACEjE. 



Elaeagnus umbellata. 

 Structure of Hypocotyl. 



The cells of the epidermis are more or less oblong in cross 

 section. There are no epidermal hairs. The outermost layer 

 of the cortex becomes somewhat thick-walled but not collenchy- 

 matous. The cortex has about six cell rows. 



The endodermis is small-celled. It remains distinct for a 

 time, but in sections of material gathered at the end of the season 

 it was not distinguished. Very little starch is found in any of 

 the tissues save in the endodermis. 



The stele is originally four-angled. A single phloem bundle 

 and two xylem bundles are placed in each of the angles. The 

 phloem soon forms a closed ring while the xylem bundles fuse 

 in pairs and increase in size. This leaves a cruciform pith. 

 The continued growth of the xylem produces a complete zone 

 surrounding, at length, a circular pith. Secretion cells in the 

 phloem are numerous. 



At the outer edge of the xylem, in old material, are a few 

 patches of sclerenchyma forming a very much interrupted ring. 



The pith is of considerable extent and is surrounded by a 

 perimedullary zone of small cells containing starch. 



Cork formation takes place far down in the cortex. 



Structure of Epicotyl. 



The epidermis consists of cells which are oblong in cross 

 section with the tangential about twice the radial diameter even 

 in very young material. The peculiar stellate trichome struc- 

 tures, well known in this genus, are abundant. 



The outer cortical cells are nearly circular in outline, when 

 seen in cross section. They are somewhat smaller than the 

 cells of the epidermis. The inner cortex is composed of large 

 cells which eventually are very much flattened owing to pres- 

 sure of the growing parts within. 



The endodermis is small-celled and contains starch. In old 

 material it was not recognized. 



The stele is circular from the first. In the youngest material 

 examined the phloem forms a complete ring surrounding about 



