338 THE FLORIST AND - 



chief source of nourishment. It has been said that the fibrils are the only 

 true roots, and that the feeding function is chiefly consigned to the lax 

 tissue of their extreme points. That this is really the case, there can be 

 no reasonable cause to doubt, or why should the success of planting depend 

 so materially upon their preservation ? it being a well-known fact, that sub- 

 jects of any size, such as fruit trees, are invariably less prolific the first 

 season after transplantation, than on the previous and ensuing years. Why 

 these little spongelets should possess the power of absorbing moisture with 

 great force, and of transmitting it to every part of the plant, is a curious 

 question, and has given rise to many ingenious conjectures. But it has at 

 length been satisfactorily answered by that clever French author, M. 

 Dutrocet. If a small glass tube, having its end covered with a piece of 

 bladder, be partially filled with gum-water, and then plunged into simple 

 water, sufficient to wet the outside of the bladder, the latter will be per- 

 meated by the water, and the volume within the tube will continue to in- 

 crease, so long as the density of the fluids on each side of the intervening 

 membrane remains unequal. " But there is also a contrary current to less 

 amount, — the interior fluid passing out to mix with the surrounding water." 

 The first and more powerful of these currents is called endosmose (flow in- 

 wards), and the second and less powerful, exosmose (flow outwards). The 

 cause of their motion was by Dutrocet referred to galvanism ; but it is now 

 more generally believed to arise from " the attraction exerted between the 

 particles of the different fluids employed, as they meet in the porous mem- 

 brane."— (Dr. Reid.) 



"Now the conditions requisite for this action are two fluids of different 

 densities, separated by a septem or partition of a porous character. This 

 we find in the roots. The fluid in their interioris rendered denser than the 

 water around by an admixture of the descending sap ; and the spongiole (or 

 spongelet) applies the place of a partition. Thus then, as long as this dif- 

 ference of density is maintained, the absorption of fluid may continue. But 

 if the rise of the sap is due to the action of endosmose, there ought also 

 to be an exosmose. This is found to take place ; for if a plant is grown 

 with its roots in water, the fluid surrounding them is soon found to contain 

 some of the peculiar substances they form, and which are contained in the 

 descending sap : thus a pea or bean would disengage a gummy matter ; a 

 poppy would communicate to the water an opiate impregnation, and a 

 spurge would give it an acrid taste." 



" Thus we see how beautifully and how simply this action, extraordinary 

 as it seems, is accounted for, when its whole history is known, on principles 

 which operate in other departments of nature." — (Dr. Carpenter.) 



