62 



PLANT BIOLOGY 



Fig. 74. — Dicotyledonous Stem of One Year at Left 



■with FIVE Bundles, and a two-year stem at right. 

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



ring. As the dicotyledonous seed germi- 

 fig. 73. — the nates, five bundles are usually formed in 



scattered j tg hypocotyl (Fig. 74); soon five more are 



Bundles or j 



Strands, in interposed 



monocotyledons between 

 at a, and the bun- 

 dles in a circle in them, and 

 dicotyledons at b. 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 



_ Fig. 75. — Fibro-vascular Bundle of 



easily determined. Indian Corn, much magnified. 



When CrOSS-SeCtionS Of A, annular vessel ; A\ annular or spiral vessel ; 



TV, thick-walled vessels; W, tracheids or 



monOCOtyledoilOUS and dl- woo dy tissue ; F, sheath of fibrous tissue sur- 



COtyledonOUS bundles are rounding the bundle ; FT, fundamental tissue 



J or pith ; S, sieve tissue : P, sieve plate ; t , 



examined Under the mi- companion cell •, /, intercellular space, formed 



by tearing down of adjacent cells ; IV, wood 



croscope, it is readily seen parenchyma. 



