Ravialey : hypocotyl and epicotyl ix woody plants. 115 



dermal hairs. No hypoderma is developed but the cells of 

 three or four outer layers of the cortex are smaller than those 

 of deeper layers. 



The endodermis is small-celled and easily recognized in 

 young stages, although at that time the cells are without starch. 

 Later starch appears in small quantities in these cells and in 

 those of the pith and phloem. 



The stele is originally four-angled and remains so for some 

 time. In each angle there is a single xylem bundle and two 

 groups of phloem ; these form a crescent-shaped mass border- 

 ing a group of cells which later develop into a resin duct. 

 After a time secondary vascular bundles are intercalated be- 

 tween the primary bundles. All finally fuse to produce closed 

 zones of phloem and xylem. 



A few small groups of sclerenchymatous cells develop at the 

 outer border of the phloem. 



The pith remains somewhat four-sided. The four original 

 xylem bundles project into it at the angles. The pith cells 

 have thin, unlignified walls. A perimedullary zone of small 

 cells was distinguished. 



Material old enough to show cork formation was not obtained. 



Structure of Epicotyl. 



The epidermis resembles that of the hypocotyl. Trichome 

 structures seem to be no more abundant. There is no collen- 

 chymatous hypoderma developed. The cells of the cortex are 

 all about the same size. 



The endodermis is not easily recognized owing to the fact 

 that in young stages it contains no starch. Later when starch 

 is present the cells have been compressed and displaced by 

 pressure from the subjacent tissues. 



The stele contains- a variable number of vascular bundles. 

 Usually there are about eight. In connection with each bundle 

 is a small resin passage, at first pointed out by Trecul [1867]. 

 In older material these resin passages become quite large and 

 somewhat flattened. The phloem and X3'lem then form closed 

 zones. 



Groups of sclerenchyma, usually consisting of only a few 

 cells, are found at the periphery of the phloem. These are 

 often located near the resin passages. 



The pith is nearly^circular, not quadrangular, and is com- 



