398 Successful Method of managing Aquatic and Bog Plants. 



as the roots come in contact with the cement or mortar of 

 the brick-work the lime is gradually dissolved, and the 

 roots penetrating through the sides loosen the bricks, and 

 thus gain more air. By this means the plants get, by degrees, 

 into the same kind of entanglement and confusion, which I 

 have adverted to in speaking of the ponds, since the sides of 

 the trenches cannot well be made stronger, than one brick's 

 thickness. These considerations led M. Schell to think of 

 wooden troughs, and he has successfully executed the idea. 



Troughs of this description are used in mines, and are 

 like channels or gutters, formed of three planks fastened 

 together at right angles, which consequently have the shape 

 of long parallelograms. If they be made of such wood, as 

 will resist the action of the water, and if they, besides, be 

 saturated with tar, they not only effectually withstand decay 

 for a great number of years, but also the encroachment of 

 the roots of the plants, which cannot act upon them, either 

 chemically or mechanically ; and their renewal may thus for 

 a long course of years be unnecessary. Now if grooves be cut 

 in the side planks, and cross boards inserted at certain dis- 

 tances, for the purpose of dividing the space into compart- 

 ments of different sizes, and if these cross boards be made 

 of the same kind of wood tarred in a like manner, by this 

 contrivance just so much room may be given to each plant 

 as may be desired, for it is only necessary to take away from, 

 or to add to these partitions, in order to contract or to extend 

 the divisions. The means are also thus afforded of managing 

 every division differently, since, for instance, to plants which 

 do not want much water (as Salvinia nutans) a deep bed of 

 earth, mixed with small pebbles, may be given, whilst others, 



