THE BRACKEX FERN 



99 



we may notice especially a number of roimded groups of 

 cells of different sizes ; these groups are the vascular bundles 

 (Fig. SI, c). It must be remembered that in a cross section 

 we see the breadth and the thickness but not the length 

 of cells; some of the cells of the vascular bxmdles are 

 many times as long as they are broad. If we follow the 

 course of the vascular bundles in the stem, we find that they 



Fig. 51. — Cross section of the stem of the bracken fern; u, epidermis; 



b, groups of very thick-walled cells which help to strengthen the stem; 



c, a vascular bundle. 



do not run parallel with one another throughout their length ; 

 here and there two bundles tmite, and at other places they 

 give off branches, so that the whole system of bundles forms 

 a network. Of the branch bundles that pass off from the 

 bundles of the stem, some nm into the leaves and others into 

 the roots, so that aU parts of the plant are connected with one 

 another by means of the network of bundles. The long cells 

 in the vascular bundles supply a path for the passage of food 

 materials from one part of the plant to another. In a plant 

 so large as the fern this work of conduction is an important 



