1 82 THE PHYSIOLOGY OF PLANTS 



cuttings those which are iu pots or boxes should receive a 

 little bottom heat in the spring ; the roots will then soon make 

 their appearance. This is especially advisable in the case of 

 Thiijopsis, Thuja, Cnprcssus, Junijjerus, Sequoia. The more 

 delicate of these should be slightly forced, so as to ripen their 

 wood sufficiently by the end of June ; still the cuttings will in 

 most cases only have formed callus by the autumn, and will only 

 produce adventitious roots in the spring- when stimulated by 

 bottom heat. 



The peculiarity of the cutting to continue the special mode 

 of growth attained by the parent plant can and is made use 

 of to form new varieties. 



Variations, such as variegated plants, lasciated specimens, 

 or double-flowering varieties, can thus be perpetuated by 

 cuttings. Of special interest are the curious juvenile stages 

 through which some Conifers pass, and which have been 

 fixed by cuttings and brought into the market as new species 

 and genera. Thus it is mentioned that to obtain Cliammcy- 

 paris squarrosa, cuttings must be made of the small shoots of 

 Biota orientalis, which appear immediately above the coty- 

 ledons, and which bear cruciate leaves. In the same way 

 cuttings of the first lateral branches of Callitris quadrivalvis 

 give rise to a quite new form. The fixed juvenile condition 

 of Cupressus sempervirens may possibly have produced C. 

 Brcgeoni ; the first shoots of Cupressus Lawsoni have not got 

 imbricate, but horizontally expanded leaves, Retinospora ericoides 

 was obtained from Chamaxyparis splia^roidea var. Andalyensis, 

 &c. 



Root-cuttings have been dealt with in the paragraph on 

 layering. They are portions of the underground axis, which 

 are stimulated by being cut in pieces to produce adventitious 

 buds. The shoot which arises from such a bud becomes an 

 independent plant of strong growth as soon as it produces 

 adventitious roots from its own tissues. Ailanthus, Aralia, 

 Paidowiiia, Rosa, Pints Malus, 3Iespihis, and others can be 

 propagated in this way, if strong pieces of their roots about 

 two inches in length are cut off either before the first shoots 

 are formed in the spring, or before the second shoots are 

 produced (July). These pieces are then planted in rows in 



