106 MINNESOTA BOTANICAL STUDIES. 



eight paired xylem bundles and a large number of groups of 

 phloem. The latter soon grow together, forming a complete 

 ring, while the xylem bundles first fuse in pairs, afterward 

 growing together into a closed zone. 



In the pericycle, alternating with the paired xylem bundles 

 there are developed four large bands of sclerenchyma which ex- 

 tend so far around that they nearly touch each other. By the 

 end of the first season these become divided into a number of 

 groups by the intercalation of parenchymatous cells. 



The pith, which is eventually of slight extent, is composed of 

 large-celled parenchyma. 



Cork formation begins rather early the first season in the 

 third or fourth cell layer of the cortex. 



Structure of Eficotyl. 



The general shape of the epicotyl is originally somewhat 

 hexagonally prismatic; it soon becomes cylindrical. 



The cells of the epidermis are originally nearly square in 

 cross section. There are numerous, long, curved, pointed epi- 

 dermal hairs. The outer two layers of the cortex become 

 slightly collenchymatous. The other cortical layers are com- 

 posed of parenchyma. 



The endodermis was not distinguished in material taken in 

 the autumn but in the young epicotyl is quite distinct. The cells 

 are rather large, similar to those of the cortical region but packed 

 with starch. 



The phloem, in youngest material examined, forms a ring of 

 tissue. There are about six principal xylem bundles which 

 soon fuse. 



A broken sclerenchymatous ring is formed which resembles 

 that of the epicotyl. No other stereom is, as a rule, produced 

 the first year. 



The pith is large and composed of cells with unlignified walls. 

 There is a small-celled perimedullary zone. 



Cork formation takes place in the hypoderma (cf. Moeller 

 [1882], p. 393). 



Comparison of Structure of Hyfocotyl and Epicotyl. 



The hypocotyl differs from the epicotyl in the absence of epi- 

 dermal hairs and of a collenchymatous hypoderma, in the pri- 

 mary structure of the stele, and in its smaller pith. 



