Ra7nalcy : iivpocotyl and epicotvl in woody plants. 93 



HORACES. 



Toxylon pomiferum. 



Struct icrc of Jlypocotyl. 



In cross section the cells of the epidermis appear radially 

 elongated. Eventually they are considerably flattened. The 

 cells of the outer cortex are similar to those of tiie epidermis. 

 There is no collenchyma developed. The inner cortex is com- 

 posed of larger cells. 



The endodermis is distinct but in material taken at the close 

 of the growing season it was not distinguished. The develop- 

 ment of pericycle is remarkable. This region is composed of 

 about six layers of parenchymatous cells resembling, in shape, 

 those of the endodermis. 



Starch is found, from the first, in the endodermis and later 

 appears in all the conjunctive tissues. 



The stele is slightly four-angled. There are, in the young- 

 est material examined, four xylem bundles and two large cres- 

 cent-shaped phloem bundles. The phloem soon forms a com- 

 plete ring as does also the xylem, but the two xylem bundles 

 first fuse in pairs. 



About this time four aggregations of small groups of scleren- 

 chyma appear in the pericycle. Eventually a nearly complete 

 sclerenchymatous ring surrounds the phloem. 



The pith is large-celled. A small-celled perimedullary zone 

 of three or four layers is present. 



Cork formation takes place in the fourth or fifth layer of the 

 cortex. 



Striicttcre of Eficotyl. 



The epidermis is composed of cells which are, at first, nearly 

 square in cross section but later are very much flattened. Ac- 

 cording to Moeller [1882] the epidermis is two-layered. 

 Numerous straight epidermal Tiairs are present ; there are also 

 some stalked glandular hairs. The cells of the cortex are 

 rather small, parenchymatous, not at all collenchymatous. 



The endodermis is distinguished with difficulty even in very 

 young material. Its cells contain starch. Starch is later found 

 in all the parenchymatous tissues. 



There is a variable number of vascular bundles ; usually 

 eight to sixteen. These soon fuse to form closed rings of 

 phloem and xylem. 



