30 



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 

 w r hich are more liable to injury by rotting. It is advis- 

 able, therefore, to add a considerable amount of sand to 

 soil in which layenngs 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 cells 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* 



