LAYERING 175 



"If the wood is tender, adventitious roots spring 

 without difficulty from the interred part, and the 

 methods already described suffice for the success of 

 the layering; but woods of dense structure are more 

 or less obstinate about taking root, and might re- 

 main in the ground indefinitely without yielding. 

 In such cases our art must intervene, based on the 

 plant's manner of living. Let us recall the effect 

 of a band drawn tightly about a stalk or trunk. 

 Above this line of strangulation the descending sap 

 accumulates more and more, since it can no longer 

 continue on its course between the wood and the 

 bark, this latter being compressed by the ligature. 

 It accumulates and produces a ring-shaped swelling 

 where the plant tries to discharge on the outside 

 the superabundance of matter arrested in its pas- 

 sage. Let this protuberance be heaped about with 

 fresh earth, and adventitious roots will speedily be 

 developed to allow the sap to continue its descent. 

 A tiny streamlet, running free, follows its channel 

 without effort and without any undermining of ob- 

 stacles. But if we obstruct its passage the accumu- 

 lating body of water will gain power to open new 

 vents for itself through the dam. Sap does like- 

 wise. Circulating freely in its natural channel, it 

 is not diverted from its course by any allurements 

 on its way; and unless the conditions present in 

 wood and bark favor the growth of new roots, no 

 sap will be expended for this purpose. But if its 

 usual passage is barred, the sap devotes its energies 

 to the formation of adventitious roots in order that 



