FUNCTIONS OF EOOTS. 43 



In Acotyledonous plants the young root is a development of super- 

 ficial cells from no fixed point, and they have been called Reterorhizal 

 (ersjos, diverse). In their subsequent progress these roots present 

 appearances similar to those seen in the stem. They frequently 

 appear in the form of fibres on the outer part of the stem, giving rise, 

 by their accumulation at the base, to the conical appearance repre- 

 sented in fig. 135, r a. 



Functions of Roots. 



Eoots either fix the plant in the soil or attach it to other 

 bodies. They absorb nourishment by a process of imbibition or 

 endosmose (flow inward), through their spongioles or cellular ex- 

 tremities. The experiment of Duhamel and Senebier, conducted by 

 inserting at one time the minute fibrils alone into fluid, and at 

 another the axis of the root alone, showed clearly that the cellular 

 extremities were the chief absorbing parts of the roots. Hence the 

 importance, in transplanting large trees, of cutting the roots some 

 time before, in order that they may form young fibrils, which are 

 then easily taken up in an uninjured condition, ready to absorb 

 nourishment. When an acorn is put into the ground, it first sends 

 down a long tap root. This is not well fitted for feeding young 

 stems and leaves, and hence numerous fibrous roots appear near the 

 surface of the ground. The more numerous these fibres the more 

 rapid the growth. The tap root is sometimes cut about seven inches 

 under ground at an early period, and this causes numerous fibres to be 

 thrown out. 



The elongation of the roots by their extremities enables them to 

 accommodate themselves to the soil, and allows the extremities of the 

 rootlets to extend deeply without being injured. Roots, in their 

 lateral extension, bear usually a relation to the horizontal spreading 

 of the branches, so as to fix the plant firmly, and to allow fluid 

 nutritive substances to reach the spongioles more easily. It is of 

 importance to permit the roots to extend easily in all directions. By 

 restricting or cutting the roots, the growth of the plant is to a certain 

 degree prevented, although it is sometimes made to flower and bear 

 fruit sooner than it would otherwise have done. The system of re- 

 strictive potting, formerly practised in green-houses, often injured the 

 natural habit of the plants. The roots filled the pots completely, and 

 even raised 1;Jie plants in such a way as to make the upper part of 

 the root appear above the soil. 



To roots there are sometimes attached reservoirs of nourishment, 

 in the form of tubercules, containing starch and gum (fig. 101), which 

 are applied to the nourishment of the young plant. These are seen 



