616 PHYSIOLOGY. 



purpose of propagating the plant which bears them, commonly compre- 

 hended under the names of offsets, stolons, runners, &c. Almost every 

 gradation of condition occurs here, between the divisible rhizomes of 

 such plants as the Daisy, Primrose, &c.,the "runners" of the Strawberry, 

 Vallisneria, Hydrocharis, &c., the offsets of House-leeks, Stratiotes, and 

 the rosette-like stolons of Epilobia, c., which approach to the axillary 

 bulbils of Achimenes, and connect all these forms with the subterraneous 

 bulbs, corms, and tubers. 



Propagation by Artificial Means. The artificial propagation of 

 plants by division is effected by a variety of processes founded on 

 the same physiological laws as the natural multiplication by de- 

 tached buds, &c. ; it also includes a peculiar class of operations, 

 in which the new plants are not converted into absolutely inde- 

 pendent stocks, but are made to assume a -pseudo-parasitical habit 

 upon other plants, whose roots furnish them with that portion of 

 their nourishment which is derived from the soil. 



In the simple propagation, advantage is taken of the vital activity 

 of the cambium-region to stimulate it to the production of roots, 

 in the gardening processes of propagation by slips or cuttings, layers, 

 &c. In the production of pseudo-parasites, as in buddmc/ and 

 (/rafting, the woody structures of two distinct plants are made to 

 become intimately blended by bringing into immediate contact the 

 cambium-structures of both, at points where the cellular tissue is 

 in an active state of development. 



Cuttings or Slips are ordinarily fragments of stems consisting of young 

 wood bearing one or more buds. These are planted in earth, and in some 

 cases require no especial care to make them produce adventitious roots 

 from the cambium-region, as in slips of Willows and many common soft- 

 wooded plants. Mostly, however, it is necessary to stimulate the vegeta- 

 tive action by a slight degree of artificial heat in all cases, however, 

 guarding against drought ; so that, as a general rule, cuttings are made to 

 " strike " root best in an atmosphere where the watery vapour is confined 

 by a glass covering. It is a matter of indifference whether a cutting 

 having a number of " eyes " or buds is planted with the head upward or 

 with the summit buried in the soil and the lower part left free. In the 

 latter case, the ordinary direction of growth of all the new shoots becomes 

 reversed. When a cutting is made, a callus of cork-cells is formed over 

 the wound, and the adjacent cells are filled with starch-grains, prior to 

 the formation of the roots. 



It has been stated above that by careful management plants may be 

 raised from cuttings of roots, and even from leaves made to produce ad- 

 ventitious buds by artificial stimulus. 



Layers only differ from cuttings in the circumstance that the fragments 

 to be detached are made to strike root before they are separated from the 

 parent stock usuallv by bending down the branches and burying them 

 in a portion of their course in the soil ; an incision is usually made into the 

 wood in the buried portion, which causes the more ready production of ad- 

 ventitious roots. An analogous operation is sometimes practised, in which 



