70 THE VEGETABLE WORLD. 
_ of various forms are employed, which are filled with earth, and 
maintained at the necessary height, the branch being placed in it 
traversing the vase in contact with the soil, as in Fig. 82. 
The soil being maintained in a humid state, the portion of the 
branch in contact with it is not slow to push forth its adventitious 
roots, which are soon present in sufficient numbers. In due time 
the branches may be separated from the parent stem, and trans- 
planted elsewhere. This is called layering by approach. 
Propagating by slips or cuttings differs from layering only in 
this, that the part of the plant employed in the process of multi- 
plication is detached at once from the parent plant, and completely 
abandoned to the powers of nature. Cut a branch even of con- 
siderable size from a willow or poplar; give it a clean sloping cut 
across a joint or node, and bury it in humid soil, it will immediately 
push out adventitious roots, and soon begin to grow a new and 
independent willow or poplar. But all plants will not so readily 
accommodate themselves to this easy mode of multiplication. 
There are some plants which will not take, to use the consecrated 
term, without the aid of many complicated. artifices ; there are 
even some which resist all means known of propagation by slips; 
in short, the slip often finds itself subject to these alternatives—to 
die of inanition, for want of sufficient moisture, or to rot from over- 
much liquid. The problem for the operator to solve, in order to 
favour the production of roots, is to establish a proper equilibrium 
between the aqueous losses to which the slip will submit, and the 
quantity of water which it absorbs; and to do so is not without its 
difficulties. But this is not the place to explain the processes 
by which these operations are successfully performed. We must 
content ourselves with remarking that the process is not confined 
to slips or cuttings of branches, as cited above. Cuttings may be 
made from rhizomes, from leaves, and even from parts of a leaf. 
But this last process is only employed for certain exotic plants; 
the inhabitants of our hot-houses which never bear fruit, and 
scarcely throw out branches. 
Layers and slips are not the only operations in which branches 
are employed for the purpose of multiplication. There is another, 
the most important of all in garden operations, namely, grating, of 
_ which we have already said a few words in connection with the 
; 
