On the Structure of Roots. 



483 



pear presently. The cortical region exhibits some striking clifFer- 

 ences in its subsequent history in different plants. In most cases, 

 especially in the roots of Dicotyledons (fig. 9), and in the branch- 

 ing roots of Monocotyledons (fig. 10), many of the epidermal 



Fig. 10. 



a, magnified fragment of a rootlet of barley, showing the fibrils; 6, highly magnified epidermis of 

 the same, showing the fibrils to be hair-like processes, produced from the epidermal cells. 



cells, at a little distance from the growing point of the root or 

 rootlet, grow out into filaments or hair-like processes, constituting 

 the ^^Jibi'ils" of roots. These are mostly invisible to the naked 

 eye, and their presence is chiefly betrayed by the adhesion of the 

 soil to them. When young roots are carefully washed and placed 

 under a magnifying glass, these fibrils are seen very clearly ; and 

 on such roots as those of barley, for instance, they exist in 

 enormous numbers. 



At the growing points of roots, the epidermis passes insensibly 

 into the mass of nascent or cambial tissue (fig. 11); but the 

 growing point of a root is not at its absolute extremity, which is 

 covered by a cap-shaped or hood-like portion of epidermis of its 

 own, continuous likewise behind with the cambial structure. 

 This cap-like sheath of the point of the root may be compared 

 with the head of an arrow, forming a firm body, which can be 

 pushed forward by the growing force behind, to penetrate through 

 the resisting soil. This cap is subject to destruction and decom- 

 position by external agencies, and is less distinctly seen in roots 

 growing in earth than in those of aquatic plants. In all cases it is 

 constantly undergoing renewal by cell-development at the back- 

 part ; and when it remains undissolved, as in many water-plants, 



