32 SOUTH AFRICAN BOTANY 
downwards. ‘The secondary roots always grow out 
nearly horizontally. Branches of the secondary roots 
are called TERTIARY roots and these will grow in any 
direction. By this arrangement of branches the whole 
of the ground is parcelled out, and the most is made of 
the space on which the plant draws for its nourishment. 
This extensive system of roots also enables the plant to 
Fra. 17.—Transverse Section of the Primary Root of the Bean showing 
a Secondary Root developing. 
p.l. Piliferous layer. p. Pith. ¢. Cortex. phil. Phloem. 0,s, En- 
dodermis. x. Xylem. (From Darwin’s “ Elements of Botany ”.) 
possess a large surface for water absorption. In dry 
parts of South Africa the roots of many herbaceous 
plants will penetrate the soil to a depth of several feet, 
in order that they can draw upon a more ample supply 
of water. 
20. Root-Cap and Root-Hairs.—The tip of a root 
ends in a cap of cells which are constantly being worn 
away on the outside and as constantly renewed from 
