122 



MINNESOTA BOTANICAL STUDIES. 



six xylem groups. The xylem bundles soon fuse producing at 

 the end of the season quite a thick zone. 



An interrupted sclerenchymatous ring is developed in the 

 pericycle. 



The pith, which is composed of large thin-walled elements, 

 is surrounded by a narrow small-celled perimedullary zone con- 

 taining starch. 



The cork is formed rather late in the season in the outermost 

 cortical layer as in other species of Elaeagnus (cf. Moeller 

 [1882], p. 117). 



Comparison of Structure of Hypocotyl and Epicotyl. 



The hypocotyl is without the trichome structures so noticeable 

 in the epicotyl ; the stele is at first four-angled instead of cylin- 

 drical ; there are four phloem bundles and eight xylem bundles 

 instead of a ring of phloem and six xylem bundles. 



At the end of the season the vas- 

 cular tissue is alike in the two regions 

 but the pericyclic sclerenchyma of the 

 hypocotyl is less abundant. Cork is 

 developed in the inner cortex of the 

 hypocotyl and in the outermost layer 

 of cortex in the epicotyl. 



MYRTACE^). 



Eucalyptus globulus. 



Structure of Hypocotyl. 



The epidermal cells, at first oblong,, 

 radially elongated, become at length in 

 cross section nearly square. The 

 cuticle, which is covered with eleva- 

 tions, appears, when young, in cross 

 section minutely serrate. 

 There is nohypoderma differentiated, but the outermost layer 

 of the cortex is smaller-celled than the layers below. The cor- 

 tical cells are large. They become flattened toward the end of 

 the season by the growth of the internal tissues. 



The endodermis is composed of small cells containing starch ; 

 it at length becomes indistinguishable. Starch is for the most 

 part absent from other tissues. Lysigenous secretion reservoirs- 

 are found in the conjunctive tissue. 



Elaeagnus 

 umbellate 



FIG. 19. 



