THE STEM. 
63 
ROOT. 
Epidermis with root hairs. 
Cortical parenchyma without 
chloroplastids. 
Fibrovascular bundles, radial, 
more numerous in monocoty- 
ledons than in dicotyledons. 
Pith usually wanting. 
STEM. 
Epidermis without root hairs. 
Cortical parenchyma with chlo- 
roplastids. 
Fibrovascular bundles, collat- 
eral (dicotyledon), or concen- 
tric (monocotyledon). 
Pith always present. 
The development of the secondary structure in dicotyle- 
donous stems is quite simple compared to that of the 
root. The cambium develops into a continuous ring, 
producing xylem within and phloem without. A phel- 
logen arises within the endodermis, and the cork re, 
places it and the overlying primary tissues. 
The arrangement of the tissues in the primary and 
secondary structures of dicotyledonous stems may be 
compared as follows : 
PRIMARY STRUCTURE. 
Epidermis. 
Hypodermis. 
Primary cortex. 
Endodermis. 
Fibrovascular bundles, radial 
and few. 
Pith. 
SECONDARY STRUCTURE. 
Cork. 
Phellogen. 
Secondary cortex. 
Fibrovascular bundles, radial, 
numerous and separated by 
secondary medullary rays. 
Pith cells frequently disinte- 
grated. 
Monocotyledonous steins, like monocotyledonous roots, 
usually grow in length, without much increase in 
thickness, except in certain cases, as in rhizomes and 
palm stems, and retain for the most part the pri- 
mary structure. Where increase in thickness of the 
stem takes place, the cells of the endodermis are altered 
in shape, and the walls of the hypodermal cells become 
thickened with lignocellulose and suberin. 
The stem as well as the root develops abnormal 
and anomalous structures, although they are not of 
