PKOBLEMS OF PEOPAGATION. 



451 



Multiplication by division is merely the following of Nature's own 

 process as seen in the increase of an Iris when, through the dying oft 

 of its older parts, separation of its newer ones occurs. 



Multiplication by layering is copying Nature by putting a mother- 

 plant in a position in which its shoots have ample opportunity of 

 rooting at the nodes, and so initiating new plants. 



But multiplication by cuttings means the isolation from their 

 previous food and water supply of parts not specially prepared to lead 

 an independent existence, and the art of the gardener is devoted to 

 calling out the exercise by the severed part oi the plant of potentialities 

 in the direction of wound-protection and organ-restitution. His pro- 

 blem is how to secure that the part used as a cutting retains adequate 

 moisture until such time as new water-absorbing organs are formed 

 through, the utilization of such food-material as is already in the 

 cutting, or which it may acquire. The water-relation is the primary 

 one. Once the severed part provides itself with the means of getting 

 a continuous water-supply it is in the state known as "struck." 

 Further developmeDt is a matter of time, and, although often slow, 

 is open to hastening by appropriate stimuli. 



The variety of constitution exhibited by plants makes the problem 

 one of some complexity. Certain plants — the so-called soft-wooded — 

 offer no difficulty. In them there is abundant water applicable to 

 callus-growth. Hard-wooded plants frequently are difficult — and the 

 reason is obvious. The key is in the water-relation. For • other 

 reasons, which I shall afterwards refer to, resinous plants and those 

 that are rich in the milky fluid called " latex " may also be difficult 

 subjects for propagation by cuttings. 



The most common method by which the gardener propagates by 

 cuttings is that by stem-cuttings, and the operation is familiar. 



Take an ordinary example of a dicotylous plant (fig. 157). A short 

 terminal portion of shoot with one or more buds is cut off from a mother- 

 plant, and the cut end is placed in a nidus of sand or other sufficiently 

 aerated material. Sooner or later, if the cutting is inserted at a right 

 depth so that aeration is adequate, callus forms as the result of wound- 

 stimulus on the basal end of the cutting in the soil. Then roots 

 emerge either from the callus alone, from the stem above the callus 

 alone, or from both. The stimulus may therefore spread from the 

 point of its application. The cutting is thus established as an inde- 

 pendent plant. The portion of shoot placed in the soil elongates at 

 the top from the terminal bud or upper lateral buds if there be no 

 terminal one, forms more branches and leaves, and we get simply an 

 extension of growth of a shoot which is now no longer attached to the 

 mother-plant. There is special interest in this, contrasting as it 

 does with the behaviour of monocotylous plants to which reference 

 will be made presently. 



Commonly, a stem-cutting includes at least one node, because it 

 is there that a shoot-bud actually in evidence or latent will be found, 

 .from .which the new extension will proceed. But in some plants. 



G G 2 



