PLANT ORGANS OR PARTS OF PLANTS. 



ROOTS. 



General Structure of the Root. — For the purpose of the 

 present study the root may be considered as the descend- 

 ing portion of the plant, and is provided with neither 

 leaves nor reproductive members. It is to be borne in 

 mind that all roots are not underground, nor are all the 

 subterranean parts of plants roots. Thus there are a 

 number of plants with aerial roots, and still more numer- 

 ous are those plants with stems that are underground and 

 which serve some of the functions of roots. 



The function of the root may be threefold: It may 

 serve the purpose of support, holding the plant to the 

 earth and giving it its proper foundation; it may serve 

 the purpose of taking in food, usually water holding 

 inorganic salts in solution ; or it may serve the purpose of 

 storing the food for the plant. Some roots serve all, 

 others only one or two of these functions. 



The study of the general shape, size, and characters of 

 roots belongs to the study of plant morphology and will 

 not be taken up in this volume.* For the purposes of 

 plant anatomy two types of root structure are to be 

 recognized. Primary and Secondary. 



Primary Structures. — In the drugs of the U. S. Phar- 

 macopoeia there are but few roots showing primary 

 structures. In such, as in the young side roots of Aris- 

 tolochia and Veratrum virtde, two fairly well differentiated 

 portions may be distinguished, the central part or central 

 cylinder (Stele), and the cortex (Extrastelar part). 



The cortex is usually provided with a layer of flattened 



* Consult Rusby and Jelliffe : Morphology and Histology of Plants. 



