98 



MINNESOTA BOTANICAL STUDIES. 



Liriodendron 

 tulipifera 



FIG. 5. 



Comparison of Structure of Hypocotyl and Epicotyl* 



The cortex of the hypocotyl is much thicker than that of the 

 epicotyl. The former region has no hypoderma ; it has four 



vascular bundles instead of six or eight 

 or more ; the sclerenchyma first ap- 

 pears in only four groups and at no 

 time is as well developed as in the 

 epicotyl. 



The pith of the hypocotyl is smaller 

 than that of the epicotyl ; it is some- 

 what quadrangular in shape. 



MENISPERMACE^E. 



Menispermum canadense. 



Structure of Hypocotyl. 



The epidermis consists of cells which 

 are square or rectangular in cross sec- 

 tion. Late in the first season they be- 

 come flat and tangentially elongated. 

 A very thick, tough cuticle develops at the same time. 



There is no hypoderma. There are about twelve layers in 

 the cortex. The cells are large. 



The endodermis consists of cells smaller than those of the 

 cortex. It remains distinct a long time, but was not distin- 

 guished in material taken at the close of the growing season. 

 The pericycle is peculiar. It is one or two layers in thickness. 

 Usually every second or third cell, when seen in cross section, 

 is without starch, although starch is present in the other cells. 

 Eventually these cells also contain starch. 



This plant is somewhat unique in the distribution of starch in 

 its tissues, for in all the different stages examined starch was 

 found in cortex, pith, endodermis and medullary rays and in 

 the pericycle except as just noted. 



The stele is quadrangular and has four primary vascular 

 bundles. These increase considerably in size as the plant 

 grows older. At the close of the growing season they are of 

 about the same extent as the medullary rays which are com- 

 posed of wood parenchyma and are full of starch. There is no 

 phloem produced the first year opposite the medullary rays. 



The pith is composed of large cells. There is a rather dis- 



