THE CAULICLE— THE STEM. 



35 



case, branches more or less according to its kind. 

 It becomes, in fact, a stem. 



The stem, like the root, has an external skin 

 overlying a cellular cortex, whilst in the centre 

 is a cylindrical strand of wood-cells, tubes, and 

 vessels of various shapes. The arrangement of 

 these several parts differs in different plants, and 

 undergoes great modifications according to age. 

 The wood-lined cells and tubes serve to strengthen 

 the plant and support it; the various vessels with 

 thinner coats serve to convey the fluids from the 

 root upwards, or from the leaves downwards, or 



sideways, according to the requirements and local 

 activity of the plant. Of the cells of the cortex 

 or rind some become "corky", and the imperme- 

 able cork preserves the tissues either from the 

 introduction of water from without or from the 

 evaporation of too much water from within, 

 according to circumstances. Others of the cor- 

 tical cells become store -places for water, for 

 starch, for chlorophyll, or other food-materials 

 and products, or for various secretions. Others 

 again stiffen into fibres, which, together with 

 the "wood" of the central cylinder, serve to 

 strengthen the plant and enable it to maintain 

 its upward direction. 



In addition to all these there is, during the 

 active growing period, a series of cells called 



Pig. 34.— Seedling Plant of Gourd (Cucurhito Pepo) with Radicle, Caulicle, and opposite 

 Cotyledons. Liberatioxi of the Cotyledons from the cavity of the Seed or Fruit Husk, 

 showing in the central figures the little peg or radicle that serves to fix the seedling. 



collectively the cambium, which, in the great 

 majority of the plants with which the gardener 

 has to deal, lies between the layers of the 

 cortex or bark and the layers of the wood, and 

 in the young state between the masses of xylem 

 or wood, and phloem or bast. The cambium cells, 

 or meristem cells as they are also called, are usually 

 relatively small, thin-walled cells, whose proto- 

 plasm is in a specially active condition, so that 

 new cells form rapidly to add to those of the 

 cortex on the one side, and to those of the wood- 

 cylinder on the other. 



From these general statements it will be seen 

 that the stem and its branches, which are merely 

 repetitions on a smaller scale of the original 

 stem, are the direct outcome and result of the 

 growth and development of the caulicle or of 

 the plumule, or of both. 



As a general rule the stem shows a tendency 

 to ascend, so as to place the leaves which it 

 bears under the most favourable circumstances, 

 and hence the great majority of the stems are 



aerial, and they vary considerably in size and 

 form. They may be soft and herbaceous when 

 of short duration, or hard and woody when 

 their life extends over a longer period. Xot 

 unfrequently they climb by encircling trees and 

 branches, as in the case of the Scarlet Runner, 

 and thus secure to their leaves all the advan- 

 tages of light and air without the expenditure 

 of much force or material in the formation of 

 a woody stem. But a great many stems or 

 branches, instead of ascending, creep along the 

 surface of the ground, or are entirely subter- 

 ranean, so that they are commonly mistaken 

 for roots. Such stems may be distinguished 

 not only by their minute anatomy, which is 

 that of the stem, but by the scales or rudi- 

 mentary leaves which they bear, and by their 

 " eyes " or buds. A potato, for instance, is 

 neither a root itself, nor the direct product of 

 a root. It is the thickened end of a subter- 

 ranean branch; the " eyes " are the buds, which 

 will eventually lengthen into shoots. Under- 



