Commercial Gardening 



thickness by the deposit of a new ring on the outside of its mass, while 

 the bark thickens by the deposit of a new ring on the inside of last year's 

 one. 



The existence of the cambium explains the art of budding a Rose, 

 grafting a scion or shoot of one Apple tree on to another, inarching a 

 young Vine on the rod of an old one, and the grafting of shoots of a 

 Clematis, Tree Pseony, and Wistaria on to the roots of another for the 

 purpose of increasing their numbers. The object in each case is to get 

 the only live portion of the scion of the tree, shrub, or climber into contact 

 with the cambium of the stem and root, respectively, used as stocks. The 

 cambium of the one coalesces or joins with that of the other, and forms 

 a new layer of wood over the old. If the grafted portion of an Apple or 

 other tree were examined after one hundred years, 

 the old cut surfaces would still be present, for 

 mature or ripened wood, being dead, never unites. 

 The whole of the wood of a tree, after it is fully 

 ripened, is dead, though it may exist for one 

 thousand years or more, protected by the bark, 

 and be of service to the tree. 



Fig. 21. Section of Dicotyle- 

 donous Stem, showing central 

 pith, three zones of wood, and 

 bark on the outside (diagram- 

 matic) 



Fig. 22. Section of Stem of Palm and Fern 



Dicotyledonous and Monoeotyledonous Stems. The above descrip- 

 tions relating to the thickening of stems and the cambium layer apply 

 entirely to Dicotyledons. The structure of a three-year-old stem is repre- 

 sented by fig. 21. Trees and shrubs are less numerous amongst Mono- 

 cotyledons, whilst herbaceous types in cultivation are very numerous. 

 Structurally they are all much alike, whether herbs, shrubs, or trees, of 

 one or many years' duration. Palms, some species of Pandanus, and a few 

 Bamboos are the only plants of tree-like habit or dimensions in the class. 

 The stem of a Palm may be taken to consider details of structure (fig. 22). 

 There is no pith in the centre, nor bark on the outside. There is a skin 

 on the epidermis, and that is permanent. The body of the tree is made 

 up of short-celled ground tissue, and distributed through this are very 

 numerous strands or bundles of fibro-vascular tissue. They are isolated 

 in the ground tissue, and when the cells, fibres, and vessels of which they 

 are composed have reached their full size, and thickened their walls, they 

 can make no further growth, as there is no cambium. Towards the circum- 

 ference of the stem the fibro-vascular bundles are the most numerous, and 



