34: THE ROOT. 



or less lengthening of the spaces between the bases of the leaves, 

 or internodes. In the Onion there is no separation ; in the Smi- 

 lax and Cane a great separation ; in the Palmetto just enough 

 to bring the leaves to the lateral surface of the stem. Fig. 25 

 exhibits the structure of the monocotyledonous stem as seen in 

 a cross-section. It is an exact exhibition of a section of the 

 Yucca. The dots are the ends of the fibro- vascular bundles. 

 Fig. 27 exhibits a longitudinal section through the axis and 

 through the terminal vesicle c v, around which all the leaves are 

 formed ; b, the base of a leaf; c, the point where the leaf b had its 

 origin ; e, compact cellular substance immediately below the gen- 

 erating surface. The fibers proceeding from the base of the 

 leaves toward the surface of the stem are smaller than the 

 others, as they contain fewer vessels. The ascent of sap in 

 monocotyledons is the same as in the dicotyledons, that is, in the 

 newly formed wood. 



Fig. 26 is a transverse section of one of the bundles greatly 

 magnified, as it is found at the base of the leaf; w, woody fiber ; 

 d, dotted ducts ; .<?, spiral vessels. The spiral vessels are always 

 toward the center of the stem. This is the structure till it ar- 

 rives at the point nearest to the center, when it becomes smaller : 

 the spiral vessels are imperfect, and finally they entirely disap- 

 pear, and- nothing remains but woody fiber. 



64, Acotyledons are such plants as increase by the elonga- 

 tion of their axis without increasing in diameter. The Ferns 

 present a type of this class of stems. On examining the stem 

 of a Fern we find it composed of cellular substance, and vessels 

 generally bearing, in some species, a very close resemblance to 

 a variety of spiral vessels. There is another variety of forma- 

 tion of Acrogens, sometimes called the centrifugal formation, as 

 exhibited by fungi and lichens, in which the formation proceeds 

 from a center, the substance being generated nearly upon the 

 same plane. Lichens may often be seen with their centers 

 dead, while the circumference is alive and growing. Fairy rings 

 are the result of this formation. 



Section 4. — Root. 



65. The root is that part of the axis of the plant which de- 

 scends in its elongation, and is the organ through which the 

 plant receives most of its nourishment, and by which it is at- 



Wbut does Fig. 25 exhibit? What Fig. 27 ? what of the ascent of sap 

 in monocotyledons? What does Fig. 26 exhibit? What of the spiral vea 

 Bela? — 64 What are acotyledonous plants ? — 65. What is the root ? 



