VEGETABLE PHYSIOLOGY— THE ROOT. 



are required. But, increasing as they do, by their points only, they insinuate themselves 

 into the crevices of rocks, or yielding parts of the soil, and afterwards, by their expansion 

 in diameter, enlarge the cavity, or when arrested by any obstacle, their advancing points 

 follow its surface until it reaches a softer medium. In this manner they rapidly extend 

 from place to place, as fast as the nourishment in their immediate vicinity is consumed. 

 Thus roots extend in whatever direction the soil proves most favorable to their growth, 

 without supposing any instinct or pre-science on the part of the vegetable, as we have 

 before stated . "The advancing extremity of the root consists of parenchyma alone, 

 but bundles of vessels and woody tissue appear in the forming root soon after their appear- 

 ance in the primordial stem above; these form a central woody or fibrous portion, which 

 continues to descend as the growing apex advances, sometimes, although not usu- 

 ally, enclosing a distinct pith, as the wood of the stem does."* We have taken the root 

 as an epitome of the whole plant, for in its whole development it produces no other parts, 

 nothing but naked branches emanating from one particular part of the root, but indiscri- 

 minately over the whole of the surperficial surface, all tending to increase the amount of 

 absorbing surface. In reply to the statement that roots produce no other organs, there is 

 this abnormal exception, namely, that of producing buds, which spring up into branches, 

 and are clothed with leaves. Although the roots are not naturally provided with buds, 

 yet, under certain circumstances, they will produce them; that for instance when 

 a poplar or apple tree, gorged with sap, is cut down, the root will send up innumer- 

 able branches. The roots of the osage Grange habitually give rise to such stems, hence 

 the utility of it in planting hedges. Some plants present a still more striking phenome- 

 na, such as the Bryophyllum, which has been known to produce buds on the margins of 

 its leaves; all such buds are said to be adventitious. 



" The root has been illustrated from the highest class of phenogamous plants, in 

 which the original root, or downward prolongation of the axis continues to grow, at least 

 for a considerable time, and becomes a tap-root, or main trunk, from which branches of a 

 larger and smaller size emanate. Often, however, this main root nearly perishes, or ceas- 

 es to grow, and the branches take its place. In some plants of the highest class, (in the 

 gourd family for example,) and in nearly the whole great classes to which the grasses, and 

 lilies, and palms belong, there is no one main trunk or primary root, from which the rest 

 proceed; but several roots spring forth simultaneously f rom the radicle in germination, 

 and form a cluster of fibres of nearly equal size. Such plants scarcely exhibit the dis- 

 tinct opposition of growth in the first instance, already mentioned as one characteristic of 

 phenogamous vegetation. Most phenogamous plants likewise send forth secondary roots 

 from the stem itself, the only kind produced by cryptogamous plants. Roots vary much 

 as regards their duration, and have been divided into three grand classes. First, into an 

 nuals, Avhich are those that spring up from the seed the first season and die; such plants 

 are composed mostly of fibrous roots, which act a powerful part in absorption, but are 

 good for nothing else. These fibres usually proceed from the sides of the tap-roots, or 

 else the whole plant divides itself at once into numerous branching fibres, such as the 

 grasses. The food which such a plant absorbs, after having been digested and elaborated 

 in the leaves, is all expended in the production of branches and flowers. The flowering 

 process and the maturation of the fruit greatly exhaust the resources of the plant, con- 

 suming all the nourishment which it contains, or in storing it up for the future oflspring, 

 and, having no accumulation of sap, the root is unable to supply the increasing demand, 

 the consequence is, it dies as soon as the growing season is over, or whenever the seeds 



* Gray's Text Book 



