62 



PLANT BIOLOGY 



FIG. 73. THE 

 SCATTERED 

 BUNDLES OR 

 STRANDS, in 

 monocotyledons 

 at a, and the bun- 

 dles in a circle in 

 dicotyledons at b. 



FIG. 74. DICOTYLEDONOUS STEM OF ONE YEAR AT LEFT 

 WITH FIVE BUNDLES, and a two-year stem at right. 



a, the pith; c, the wood part ; b, the bast part; a. one year's growth. 



ring. As the dicotyledonous seed germi- 

 nates, five bundles are usually formed in 

 its hypocotyl (Fig. 74) ; soon five more are 

 interposed 



between 

 them, and 

 the multi- 

 plication continues, in 

 tough plants, until the 

 bundles touch (Fig. 74, 

 right). The inner parts 

 thus form a ring of wood 

 and the outer parts form 

 the inner bark or bast. A 

 new ring of wood or bast 

 is formed on stems of di- 

 cotyledons each year and 

 the age of a cut stem is 

 easily determined. 



When cross-sections of A 

 monocotyledonous and di- 

 cotyledonous bundles are 

 examined under the mi- 

 croscope, it is readily seen 



FIG. 75. FlBRO-VASCULAR BUNDLE OF 



INDIAN CORN, much magnified, 

 annular vessel ; A', annular or spiral vessel ; 

 TT, thick-walled vessels ; W, tracheids or 

 woody tissue ; F, sheath of fibrous tissue sur- 

 rounding the bundle ; FT, fundamental tissue 

 or pith ; S, sieve tissue : f, sieve plate ; C, 

 companion cell ; /, intercellular space, formed 

 by tearing down of adjacent cells ; W ', wood 

 parenchyma. 



