120 



MINNESOTA BOTANICAL STUDIES. 



There are four primary vascular bundles. Other secondary 

 bundles soon become intercalated and finally complete rings of 

 phloem and xylem are produced. 



A single group of sclerenchymatous elements is formed at 

 the outer edge of each primary vascular bundle. By the end 

 of the season other smaller groups are also present. 



The pith finally becomes very small. Sometimes, by the 

 projection into it of two of the vascular bundles, a line of xylem 

 extends nearly across it. There is no perimedullary zone. 



The cork cambium, as in other species of Vitis (cf. Flot 

 [1889]), is formed about the close of the first season in the 

 pericycle. 



Structure of Epicotyl. 



The epidermal cells are square in cross section, becoming at 

 length flattened. The cuticle is like that of the hypocotyl. A 

 well-differentiated collenchymatous hypoderma is present. The 

 other cells of the cortex are parenchymatous. 



The endodermis contains starch and is, therefore, easily dis- 

 tinguished. Toward the end of the season starch is also found 

 in the pith. The number of primary vascular bundles is var- 

 iable. Usually there are more than eight. At an early time 

 closed zones of phloem and xylem are produced. 



A broken ring of sclerenchyma is developed toward the end 

 of the first year in the pericycle. 



The pith is thin-walled and large- 

 celled. A definite perimedullary zone 

 was not distinguished. 



The cork, as in the hypocotyl, is 

 of pericyclic origin ( cf. Moeller 

 [1882], p. 207). 



Comparison of Structure of Hypo- 

 cotyl and EpicotyL 

 The hypocotyl has a thicker cortex 

 than has the epicotyl. It has but four 

 primary vascular bundles instead of 

 eight or more. It has four large 

 masses of sclerenchyma in the peri- 

 cycle and a few smaller ones instead 

 of a more nearly continuous scleren- 

 FIG. 18. chymatous ring. 



VitiS cordifolia 



