ITS THEORETICAL STRUCTURE. 135 



transfers to the soil in the form of cuttings (which are merely buds 

 with a small piece of the stem), where they throw out roots from 

 the base and grow into independent plants. As the bud, excited 

 by warmth and moisture, developes upwards into a stem, just as it 

 would have done into a branch had it remained in union with the 

 parent, so it strikes root downward from the base of the cutting, 

 and the woody fibres of these roots, taken together, may be traced 

 back directly to the bud. Evidently the fibres, which may be 

 traced as wood from the bud down to the base of the cutting, are 

 prolonged beyond into roots. The resemblance between the orig- 

 inal stem and the branches it bears, therefore, holds good through- 

 out. As the downward growth of the original stem gives rise to 

 roots, so the downward growth of the lateral buds, when they grow 

 in connection with the parent stem, contributes to the wood be- 

 neath, and at length to the roots. In layering (167), the gardener 

 well knows that roots strike more readily when an incision is made 

 into the stem where it is covered with the soil. The evident ex- 

 planation is, that the descending woody growth, arrested by the 

 incision in the cellular callus that forms there, is forced, as it 

 were, to strike at once into the soil, instead of pursuing the longer 

 course through the main trunk to the same ultimate destination. 

 This is the very economy of shrubs and trees which naturally 

 multiply by suckers and stolons ; from which the singular Ban- 

 yan (Fig. 119), that in time spreads into a grove, 



" High over-arched, with echoing walks between," 



in no wise differs, except that the roots strike and the whole pro- 

 cess goes on high in the open air. In this case, portions of the 

 new wood merely take another and nearer course to the ground in 

 the form of aerial roots, which in time produce additional trunks, 

 instead of continuing their adhesion to the branches, and contribut- 

 ing to the increase in diameter of the main trunk. The additional 

 trunks thus produced, and which eventually, by separation and 

 the decay of the original trunk, may form the stems of independ- 

 ent trees, exactly represent the outer and newer layers of an ordi- 

 nary tree, the main stem representing the old and often decay- 

 ing centre. Further and very striking illustrations are furnished 

 by those curious stems of Barbacenia, Kingia, and some Lycopo- 

 dia, in which numerous aerial roots, instead of striking off free 

 from the exterior, descend under the bark or rind, where they are 



