THE LOWER FORMS OF LIFE. 9 



fibrils spring from the axis, where they are .covered with a cellular 

 sheath. The centre fibril (a, Fig. 3) being generally considered as 

 replacing the principal root, it only remains to add that the root or 

 rootlets is lengthened or extended laterally by cellular additions to 

 its extremity. In plants whose branches spread, the roots are wisely 

 ordained to spread also, and thus retain a powerful attachment in 

 the soil. In the wheat-plant the roots do not extend or branch out 

 far laterally, because the stem, being branchless, does not require 

 such a provision. 



Having thus formed a clear idea of a root its branches, cover- 

 ings, cellular texture, and sponge-like extremities, let us now notice 

 how it performs its functions. In other words, how does the wheat- 

 plant feed 1 ? 



It is, of course, obvious that the feeding of plants, whether by 

 their roots, or other means to be treated of hereafter, must have 

 reference to their growth and perfection, and it is with this connec- 

 tion in view that I shall treat the subject here. Let us at present 

 observe the functions of the root. They are connected with one of 

 the most interesting of natural laws. 



If a glass cylinder be filled with a solution of sugar or chemical 

 salts, and the end covered over with a piece of bladder, and if this 

 cylinder be then inverted and placed in a jar of pure water, the 

 following change will take place : two currents will be established 

 through the bladder, one conveying a part of the solution of sugar 

 out of the cylinder, the other a part of the water out of the jar into 

 the cylinder, and these currents are termed in reference to their 

 directions in or out, "endosmosis" and "exosmosis." Now the root 

 of the plant is a cylinder, containing in its vascular vessels a fluid 

 having a density different from the water containing the plant's food 

 in the soil. The vascular vessels, in fact, contain the excretions of 

 the plant in solution and thus a beautiful interchange of that 

 which is useless with that which is all important as food, is set 

 up. The excretions pass out by exosmosis through the membrane 

 covering the spongioles, while the food passes in through the same 

 membrane by endosmosis. It is impossible to conceive anything 

 more interesting or suggestive than the application of this well- 

 known physical law to the means by which plants feed. 



We shall see, by and by, as we proceed upwards in the scale of 

 nature, that all the great physical laws known to man and applied 

 by him in works of art, have been anticipated in the organisation of 

 living things. 



It is thus, then, that the roots convey the alimentary matter 

 found in the soil into the plant. 



Let us now examine how the stem grows. 



