28 



ANALYTICAL CLASS-BOOK OF BOTANY. 



in which it is placed. The Stem, for the most part, de- 

 velopes in the open air, and in that free element elon- 

 gates without interruption through its whole extent ; 

 while the Root, living in a denser medium, must have a 

 corresponding difference of habit. Instead of projecting 

 forward its wh(jle length, it insinuates itself, point by 

 point ; and as if Caution had been a natural companion 

 of the Darkness, it thus creeps along, opening a way, and 

 finding a space for itself, which otherwise it could not 

 attain. By this method, also, it is able to avoid any 

 obstacle, by winding round it. But if it grew like the 

 stem by a uniform projection of its whole substance, the 

 vital elements would be arrested in their flow, by every 

 obstacle with which any portion of the growing part 

 might come in contact. The active juices thus thrown 

 back, would accumulate ; the growth would only develope 

 swellings and contortions ; repeated deformities would 

 occur ; and the symmetry of the plant, and perhaps its 

 health also would be destroyed. But the Wisdom that 

 leadeth the little lambs on the hill-side guideth the Root 

 as well ; and thus led it never goes astray in the dark. 



FUNCTIONS OF THE EOOT. 



162. Mechanical fixture, by which it maintains and 

 counterbalances the superincumbent stem and branches, 

 is the first, and most obvious function of the Root. But 

 if you examine closely, you will find that it has also 

 other oflSces, which may properly be termed vital. The 

 most important of these is 



163. Absorption — or the power of sucking from the 

 soil the liquids and gases which are essential to the life 

 of the plant. This office is performed chiefly, if not 

 entirely, by the fibrils, or small hair-like processes with 

 which the root is abundantly clothed. These parts, 

 having no epidermis at their extremities, absorb liquids 

 with a great deal of power, until the root is completely 

 saturated with moisture from the surrounding soil (164). 

 The way in which this force operates was long a subject 

 of much doubt and mystery. The ascent of the sap is 

 directly contrary to gravitation ; and thus one of the 

 highest laws of Nature was supposed to be contravened 

 by the Vegetable Economy. The theory of capillary 

 attraction was objectionable, because there are no con- 

 tinuous tubes in the vegetable -frame, but only closed 

 cells, and short, interrupted passages. Yet these very 

 cells, closed by membrane, are now found to combine all 

 the circumstances necessary to a, maintenance of that 



Leading subject. Dcflne Physiology. To ^bat does it chiefly relate ? How 

 iloes the Stem grow ? The Eoot ? Keason of tho difference. If it grew like 

 ilie stem, what would happen ? First and most obvious function of the Root? 

 Most important function f By what organs chiefly maintained ? Theory of 



mode of circulation which was discovered by Dutrochet 

 and is termed Endosmose and Exosmose. This, be- 

 ing at present the accepted theory, and one which, as far 

 as it goes, satisfactorily accounts for one of the most re- 

 markable and important processes in Nature, something 

 should be known about it. 



165. Theory Explained. — Two liquids of different 

 densities separated by a membrane, attract each other, 

 and currents will be established between them ; but that 

 from the denser to the weaker liquid will be strongest, 

 in proportion to the difference of density between the 

 two. The principal current is called Endosmosb, or 

 inward flowing, the other Exosmose, or outward 

 flowing. 



166. The Experiment. — Immerse a bladder partly 

 filled with milk, or a weak solution of sugar, in a vessel 

 of pure water, and the bladder will be gradually filled, 

 by the action of endosmose ; while at the same time the 

 water in the vessel will be slightly sweetened, or whiten- 

 ed, by a transudation of the denser liquid, through exos- 

 mose. If a glass tube having the lower end closed with 

 membrane be used, you can witness the progress of the 

 experiment. 



167. Application. — The vegetable cells are the 

 tubes closed with membrane — cellulose — which, it will 

 be remembered, is permeable by liquids (32). These 

 contain assimilated juices, which, being mingled with the 

 crude sap, or lymph, render it more dense than the 

 water on the outside of their walls, which being attract- 

 ed toward the denser liquid by this law that always 

 tends to equilibrium of densities, flows inward — and 

 this is Endosmose. 



168. But that the counter-current, Exosmose is also 

 established, is clearly shown by two facts. First, a 

 plant grown in water always imparts some of its peculiar 

 properties to the liquid which it inhabits ; and secondly, 

 we find by a careful analysis of the soil round any plant, 

 that the earth is more or less impMgnated with its pecu- 

 liar properties, neither of which could be if the liquids 

 of the plant did not flow outward. 



169. But though all this is, almost beyond a doubt, 

 true, there is yet a higher truth that should not be lost 

 sight of. The Vital Principle is still, and ever must be, 

 superior to merely mechanical laws ; and to a consider- 

 able extent holds them in obedience to itself. Putrochet 

 considered Galvanism as the agent of transmission ; and 

 probably there are several agencies concerned. The 



Capillary attraction, why objectionable ? Theory now generally adopted, called 

 what? Explain. Meaning of Endosmose ? Exosmose? Describe experiment. 

 Application. What force superior to the mechanical ? What forces probably 

 assist the operation ? Dutrochet considered the a^ent of transmission what ? 



