Igg Transactions op the American Institute^ 



miual points only of the fibrous roots are supplied, and are sub- 

 jected to chemical changes during their passages through the 

 plant, but enter as elements of the sap and remain as tissues of the 

 plant, being in no way exerted. As no means are supplied for a 

 plant to get rid of deleterious substances if once absorbed, and 

 as neither human reason nor animal instinct is given to plants to 

 guide their rejection of such food as is unsuited to their growth, a 

 wonderful selective power is given the plant, in the absorbent 

 action of its roots, whereby it takes up such portions only of mine- 

 ral solutions, both in kind and quantity, as the plant needs for its 

 proper growth, however great the excess of its favorite and needed 

 elements may be in the soil in which it stands. Different plants, 

 growing in the same soil, will each select the mineral salt held in 

 solution by the water in the soil, that it needs for its own proper 

 growth; a familiar example is the selection of silex by wheat, and 

 of calcareous substances by peas, when growing together, and the 

 fact is easily shown by prior and subsequent analysis of the soil 

 and an analysis of the ashes of the wheat and peas. The first step 

 in the circulation of sap in plants is its absorption by the roots, 

 and as the root is the basis of the plant and the principal organ by 

 which it is supplied with nourishment, it is of first importance to 

 consider its parts and mode of action. Its parts consist of the 

 caudex or main body of the root — the fibrils or finer branches sent 

 off from the caudex, which are the true roots, and the spongioles, 

 which are the tender and delicate extremities of the fibrils or grow- 

 ing points, and this accounts for the facility with which these little 

 rootlets penetrate crevices and force their way into the hardest 

 earth. The fibrils consist of minute bundles of vasiform tissue, 

 enclosed in a loose cellular epidermis, except at the extremities, 

 where the tissue is naked and becomes exceedingly loose and 

 spongy (whence the name spongioles, a diminutive of sponge), and 

 has the property powerfully to absorb water. The root does not 

 absorb moisture by its whole surface, but only by the spongioles 

 at the extremities of the fibrils, Avhere the pores are not obstructed 

 by the epidermis. The members of the society will, therefore, 

 readily see, not only the great importance of securing an abundance 

 of these fibrils or true roots in all trees which they purchase, but 

 also that the tender spongioles — the living flesh as it were — or sensi- 

 tive points of the plant, exposed as they are, without covering of 

 epidermis or skin, shall not be dried up or injured. The causes of 

 the absorption of fluids by the roots, and what forces are engaged 



