TRANSFER OF MATERIALS IN PLANTS 



175 



Medullary 

 ay 



cells, some consisting of series of cells from which the end 

 walls have disappeared, leaving long, continuous channels. 

 Some of these vessels are illustrated in Figs. 10 and 62. 



The sap-carrying ves- 

 sels of the root are 

 continuous with similar 

 tubes found in the stem. 

 The tubes are found 

 arranged side by side in 

 bundles rather than in 

 single strands (Fig. 62). 

 The bundles of vessels 

 and fibers, in many 

 plants, are easily sepa- 

 rated from surrounding 

 cells, or pulled out. In 

 celery these bundles 

 make up the "strings," 

 and when you pull up a 



FIG. 63. Structure of a woody stem 



leaf of the plantain, you 

 can see the so-called 

 nerves that stick out of 

 the broken end of the 

 leafstalk, which are also 

 fibrovascular bundles. 



In woody plants the 

 fibrovascular strands are 



Diagrammatic view of piece of two-year-old black- 

 berry stem, showing the central pith, surrounded by 

 the wood of the first and second years, the bark, and 

 the epidermis E. The wood is made up of wood 

 fibers, Wf, and vessels, Pd, representing a pitted 

 duct. Between the wood and the bark is the grow- 

 ing, or cambium, layer, and this is connected with 

 deeper layers by means of the Medullary rays, Mr. 

 Under the skin are some green cells, Gc, and running 

 through the bark cells C are bast fibers, Bf, as well 

 as bast vessels, which are not shown 



compacted into solid 



cylinders ; these make up the successive layers of wood (Fig. 63). 



The fibrovascular bundles branch and divide so that they 

 reach into all the twigs and leaves. In the leaf they branch 

 again and constitute the so-called veins, or nerves, of the 

 leaf blade (Fig. 64). 



The food sap does not pass through the same tubes as 

 the water and salts from the roots. The manufactured food 



