Stem and Root Structures 



79 



roots extending in four rows nearly its entire length. At the 

 base of each root a slender 

 horizontal slit is seen. 



A cut across the carrot 

 shows a circle of tissue 

 about midway between 

 centre and circumference ; 

 this region is actively divid- 

 ing and adding to the thick- 

 ness of the root. A carrot 

 which has been left for a 

 time in methyl blue will 

 show traces of blue in the 



Fig. 76. — Root of carrot, cross section. 

 L, Cork ; tp, secondary parenchyma ; 

 sx, secondary xylem. 



part enclosed within this circle which indicates, as in the stem, 

 the region of wood vessels. They are surrounded by an abund- 

 ance of storage tissue of which the carrot largely consists. 

 Although the carrot has been immersed, a layer of cork pre- 

 vents the surface of the carrot from absorbing the solution. 



If a cross section is stained with iodine, the medullary rays 

 may be traced by the starch they contain. This is most abun- 

 dant outside of the active ring where the rays extend through 

 the phloem. 



Either a cross section or one cut lengthwise shows the 

 lateral roots extending to the central portion of the root. Un- 

 like leaves and branches, they arise in deep seated tissue and 

 make their way through the cortex of the main root. 



While points of resemblance may be seen between a stem 

 and a root, they show in their general form essential points of 

 difference. 



1. A root is protected by a root cap which is constantly 

 worn away as it pushes its way through the soil. A stem is 

 protected by the young leaves which form the bud. 



2. Roots give rise to roots, stems [)roduce stems and also, 

 unlike members, leaves. 



3. Lateral roots arise within deep-seated tissue (endogen- 

 ously) ; lateral branches and leaves arise from surface tissues 

 (exogeiiously). 



4. The stele in roots is relatively small, that is, the rigid 



