THE GENERAL CHARACTERISTICS OF PLANTS 1 
Some of the Tissues in the stem for instance, are the outer 
protective tissue or EpmeErmis, the soft region beneath the epi- 
dermis and in the pith of the stem or PARENCHYMA, the woody 
& 
gre i " ’ yng 
SS 
Be 
sie i ll 
Fic. 3.—-Cross section of a representative portion of the stem of a clover (Tri- 
folium) illustrating the tissues and tissue regions found in a stem of an herbaceous 
dicotyledon. X 80. ¢p., epidermis or outer protective tissue; s, stoma, ss, sub- 
stomal air-space, co, primary cortex containing parenchyma, f, sclerenchyma 
fibers, ph, phloem containing sieve tissue, ca, cambium, and x, xylem of an open 
collateral fibrovascular bundle; mr, medullary ray composed of parenchymatous 
cells, m, medulla or pith composed of large parenchyma cells and small angular 
air-spaces. Note the xylem contains long conducting tubes, here shown in cross 
section as large open circular areas arranged radiately, which conduct water 
upward through the plant axis. 
portion which gives support to the stem or SCLERENCHYMA (stony 
tissue), the water tubes which conduct crude sap upward or 
TRACHEARY TISSUE and the sieve tubes and phloem cells which 
carry elaborated sap downward or Steve Tissue. 
