Structure and Work of Stems 



35 



thick-walled, woody fibers, arranged with 

 overlapping ends cemented together, thus 

 stiffening the stem. The water-conducting 

 vessels are surrounded by these woody 

 fibers. In some grasses and grass-like 

 plants, the water vessels and wood fibers 

 are united into strands forming the 

 ''threads/' or fibro - vascular bundles, 

 embedded in a mass of soft pithy tissue. 

 This condition is well illustrated in the 

 stalks of corn. The strands (Fig. 23) in 

 the pith are bundles of woody fibers sur- 

 rounding the water-conducting channels. 

 Plants having the veins of the leaves 

 arranged like a net have the water-con- 

 ducting vessels in the woody part. (Fig. 

 22.) In young stems they exist as separate 



Fig. 23. Corn- 

 stalk, showing 

 fibro- vascular 

 bundles, or 

 " threads." 



Fig. 24. Cross-section (B) and longi-section (A) of stem, greatly magnified. 

 P, pith; d, d, water ducts; m, medullary rays; w, woody portion of stem; 

 c, delicate cambium or growing cells; s, phloem of food-conducting cells; b, 

 hard fibers; ck, cortex; e, epidermis. 



