FIBROVASCULAR BUNDLES IN LEAVES 



The living cells in the blade of the leaf receive water and dissolved minerals and 

 send food through an intricate system of small veins, which extend to all regions of 

 the leaf. These small veins, or fibrovascular bundles, connect with larger veins in 

 the leaf, the stem and the roots 



separate threads— for example, flax, hemp, sisal, linen, and so on. Chil- 

 dren like to pull the "nerves" out of the leaves of plantain, and we are all 

 familiar with the "nerves" in the celery stalk and with the strings in 

 cornstalk. 



The arrangements of fibrovascular bundles in stems and leaves are so 

 characteristic that they enable us to recognize at once members of the two 

 mam divisions of seed-plants, namely, monocots and dicots (see Appen- 

 dix A). In the monocots, plants having but one cotyledon in the seed, the 

 veins run almost parallel, as in grasses, lilies and bananas. In the leaves of 

 dicots, plants having two cotyledons in the seed, the veins run into each other, 

 forming networks, as in the potato plant, the elm, or the geranium (see 

 illustration above). 



Types of Stems In monocotyledonous plants fibrovascular bundles are 

 scattered throughout the stem (see illustration, p. 146). They are much 

 more numerous toward the outside. The water-conducting vessels (xylem) 

 are toward the center of the stem, and the food-conducting cells (phloem) 

 are toward the outside. Between the xylem and phloem tubes and sur- 

 rounding them are the thick-walled woody fibers. 



145 • 



