456 JOITENAL OF THE RC^'AL HORTICULTURAL SOCIETY. 



terminal growth, and that means rapid growth. From the beginning 

 the monocotyl displays lateral growth, and that means sluggish growth. 



The habit thus early shown by these two classes of plants appears 

 to be impressed upon them and reappears in the stages of vegetative 

 propagation by cuttings. The terminal shoot of the dicotyl extends as 

 the new plant from the rooted cutting. A lateral bud develops as the 

 new rooted plant in the monocotyl and the terminal portion of the 

 cutting dies. 



We may emphasize further these relationships and contrasts by 

 pointing out that whilst a wood-cambium such as occurs in dicotyls 

 is generally absent from monocotyls, some tree and shrubby forms — 

 for example, Dracaena (fig. 167) and Witsenia — make a wood-cambium 

 of a special kind. Correlated with this divagation from the ordinary 

 monocotylous type in the direction of the dicotylous the terminal 

 portion of the shoot when cuttings are made elongates and forms an 

 extension of the severed shoot after the fashion of the dicotyl. 



Any root with adequate substance and food-supply may be used 

 for propagation under suitable stimuli. Propagation by root-cuftings 

 is governed by the same principles as are involved in stem-cuttings. 

 There is, however, this difference in the plant part concerned. The 

 root is an organ that is normally forming new branch roots — absorbent 

 organs. Its reserve in respect of these is immense. What the 

 gardener requires is that the severed root forms shoot-buds such as many 

 produce when in normal relationship. The shoot-buds are new forma- 

 tions in the cutting. The cut surface of the cutting in dicotyls forms 

 callus as in the shoot, and the bud may take origin in the callus. 

 Otherwise the bud develops from the pericycle out of which 

 daughter roots arise. There are here no nodes and internodes, as in 

 the stem offering regions of selection. Any short portion of the root 

 treated like an ordinary stem-cutting suffices. Through no feature of 

 its organization is the consequence of the colonial construction of the 

 plant more evident than in this propagation by roots. 



Comparative experimental work with root-cuttings has not been 

 extensive, and we have much to learn about the stimuli conducing to 

 shoot-formation from roots. By the gardener the method has been 

 found useful when propagation by stem-cuttings has been slow, for 

 example in Spathodia campanulata, or difficult as in Calycantlius, 

 Cladrastis, and Ailafithus, and in dealing with herbaceous plants like 

 Vrosera, 'from which stem-cuttings cannot readily be obtained. 



Before leaving the subject of root-cuttings I ought perhaps to say 

 that in the term " root " I refer to the true root. It is difficult when 

 reading gardening literature to determine in many cases the sense in 

 which the word " root " is used — w^hether as including all underground 

 parts of plants or the root in its botanical sense alone. 



We have seen how in Nature, for example in Bryophylhim, vege- 

 tative propagation may be carried on through the leaf alone, and I 

 have described how a leaf may be ancillary to the stem in the case of 

 a stem-cutting by assisting in the formation of roots if it be left at 



