THE ROOT 15 



The ripened seed is the product of reproductive processes, and the 

 starting point in the life of all Phanerogams. The living part of the 

 seed is the embryo, which, when developed, consists of four parts, the 

 caulicle, or rudimentary stem, the lower end of which is the beginning 

 of the root, or radicle. At the upper extremity of the stem are two 

 thickened bodies, closely resembling leaves, known as cotyledons, and 

 between these a small bud or plumule. 



The function of the cotyledon is to build up nourishment for the 

 rudimentary plantlet until it develops true leaves of its own. 



The Root 



The root is that part of the plant that grows into or toward the 

 soil, that never develops leaves, rather rarely produces buds, and 

 whose growing apex is covered by a cap. 



The functions of a root are absorption, storage and support. Its 



hair 

 Fig. 12. — Cross-section of rootlet in the region of the root hairs. {From Steiens.) 



principal function is the absorption of nutriment and to this end it 

 generally has branches or rootlets covered with root hairs which largely 

 increase the absorbing surface. These root hairs are of minute and 

 simple structure, being merely elongations of the epidermis of the root 

 back of the root cap into slender tubes with thin walls. 



The tip of each rootlet is protected by a sheath- or scale-like cover- 

 ing known as the root cap, which not only protects the delicate grow- 

 ing point, but serves as a mechanical aid in pushing its way through 

 the soil. The generative tissues in the region of the root cap are: 

 PLEROME, producing fibrovascular tissue; periblem, producing cortex; 

 DERMATOGEN, producing epidermis; and calyptrogen, producing the 

 root cap. 



