20 
delicate shrubs, as well as for climbers like Clematis. A 
similar process has been found advantageous for many 
herbaceous plants such as Violas, Carnation and Pinks. 
In these cases, however, it is usual to make a slight 
incision in the buried portion of the shoot, which should 
always extend to one of the knots or joints. Such an 
incision stimulates the production of roots, particularly at 
the end furthest removed from the parent plant. This is 
no doubt due to the accumulation at this point of food 
material which has been produced by the leaves at the tip 
of the layered shoot, the food material being unable to 
be carried across the incision. Even in dealing with 
shrubs it is sometimes found advisable to make an in- 
cision partially across the branch which is to be layered, 
and to peg it down so as _to keep it in position until 
the new roots are formed. It is of great importance that 
the soil in which the new roots are to form should be well 
aerated, more particularly in the case of herbaceous plants 
which are more liable to injury by rotting. It is advis- 
able, therefore, to add a considerable amount of sand to 
soil in which layerings are to be embedded. 
In the case of upright stems or branches, which are far 
above the soil, the production of adventitious roots can be 
promoted by removing a ring of outer tissues to the depth 
of the wood, and then tying a handful of wet moss round 
the shoot. Such ringing causes the food material formed 
in the upper part of the plant to accumulate above the 
wound, and this promotes the rapid development of roots. 
When these have become sufficiently established the 
rooted portion of the stem or branch may be severed from 
the parent. 
In many plants the formation of adventitious roots is 
so rapid that shoots completely detached from a plant 
can establish themselves as cuttings, producing their own 
roots when placed in suitable conditions. In all cases in 
which cuttings are made the first need is to cause the cover- 
ing in, that is, the healing of the cut end of the shoot. 
This is done by the development from the actively grow- 
ing cells of a peculiar wound tissue, called callus, which 
by growing over the wound and developing a layer of 
cork, prevents the destruction of the exposed celis and 
the entrance of harmful bacteria. The growth of callus 
is promoted by the aeration of the tissues, and it is there- 
fore important that the soil in which cuttings are placed 
