276 ON VEGETABLE PHYSIOLOGY. 



sists of several ramifications, from the sides and extremities of which, 

 without any apparent order or regularity, proceed an indefinite number 

 of delicate fibrils with spongy points. Now these fibrils are the 

 only true roots, and to their soft extremities (spongelets) is consigned 

 the whole office of absorbing fluid ; the more woody portions of the 

 root merely serving as canals, to convey the fluid thus obtained to the 

 upper parts of the plant. The roots generally pierce the soil in a 

 downward or horizontal direction, according to the individual habit, 

 but more especially in that course which offers the least resistance, and 

 yields the greatest quantity of soluble food. Hence the propriety of 

 mulching is by some gardeners called into question, because the rich- 

 ness of the mulching material, and the warmth produced by its fer- 

 mentation, has a tendency to attract to the surface the young fibrils. 

 And then upon the removal of the manure employed in the operation, 

 their extremely succulent and tender tips become exposed to the in- 

 fluence of draught, &c, than which nothing can be more injurious, as 

 it quickly destroys their absorbing power, and thus deprives the plant 

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

 are the only true roots, and that the feeding function is chiefly con- 

 signed to the lax (issue of their extreme points. That this is really 

 the case, there can be no reasonable cause to doubt, or why should 

 She success of planting depend so materially upon their preservation ? 

 it being a well-known fact, that subjects 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. Du- 

 trocet. 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 permeated by the water, and the volume within the tube will con- 

 tinue to increase, 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 inwards), and the second and less 



