34 



THE GARDENER'S ASSISTANT. 



carrot, the cortex or rind of these tap-roots in- 

 creases very much in thickness, owing to rapid 

 multiplication of the cells. In these cells a large 

 quantity of water and food-materials is stored up, 

 so that the plants are thereby protected against 

 the effects of drought, whilst the food-materials 

 are available for use when growth is going on 

 actively. Moreover, they are serviceable as food 

 for man or animals, and for this reason they are 

 cultivated. Sometimes, as in the Dahlia, it is the 

 branches of the roots which become tuberous and 

 store up in their cellular tissue food-materials for 

 next season's consumption (fig. 33). Should the 

 central rather than the cortical parts of a tap- 

 root become developed, and should they become 

 woody rather than succulent, then the roots be- 

 come Avoody as in trees. Such roots not only 

 act as conduits and store places, but their size, 

 their strength, their manifold and widely-spread 

 branches, enable them to act as efficient anchors 

 and to prevent uprooting by storms. The old 

 woody parts of the roots are never clothed with 

 root- hairs, and have nothing to do with the 

 absorption either of liquids or of gases, those 

 functions being exclusively confined to the root- 

 hairs, or to the finest root-fibres. 



Such, in very general terms, are the structure 

 and office of the root. In detail there are great 

 differences in form and internal structure, but 

 none of them affects the general principle of 

 root-action, nor, so far as we know at present, 

 are the diversities of internal structure of direct 

 practical importance to cultivators. 



The young gardener, however, will do well to 

 pay great attention to the different forms and 

 degrees of branching in roots, for it is evident 

 that his treatment of plants must vary con- 

 siderably according to the nature of the roots. 

 To expect a fine, delicate-rooted plant, like a 

 Heath, for example, to thrive in dense clay is to 

 expect the impossible. Indeed such matters as 

 the choice and composition of soils and composts, 

 the securing adequate drainage, the method of 

 potting, and the many circumstances regulating 

 the administration of water, are all directly 

 dependent on the nature and office of the roots. 



The root as above described is the seedling 

 root or its direct continuation. The seedling 

 root, however, very often perishes, and secondary 

 roots are formed to supply its place. These 

 secondary roots, which emerge from the base of 

 the stem, or even from the leaves, have essen- 

 tially the same structure as the seminal root 

 and perform the same offices. "Adventitious 

 roots" of this character are very common on 

 the stems of vines, and generally indicate either 



that the atmosphere of the house is too moist 

 and stuffy, or that the true roots do not obtain 

 sufficient moisture from the border, [m. t. m.] 



CHAPTER IV. 



THE CAULICLE— THE STEM. 



The Primary Bud or Plumule — The Stem — The 

 Cambium — The Wood — The Bast — Various 

 Forms of Stems: Bulbs, Tubers, &c— Structure 

 op Stem. 



Referring again to the seedling plant of pen- 

 stemon or the gourd (fig. 34), it may be noticed 

 that the root tapers gradually downwards into 

 the soil, whilst the two seed-leaves (cotyledons) 

 are borne aloft upon a slender shaft which is 

 perfectly cylindrical, wholly unbranched, and 

 destitute of root-hairs. To the naked eye, then, 

 this little shaft differs materially from the root. 

 In internal structure it differs still more. It is, 

 in fact, the first representative of the stem, and 

 is known as the "caulicle", or sometimes, from 

 its position below the two seed-leaves, as the 

 hypocohjl. Its object is to upraise the two seed- 

 leaves and enable them to be exposed to the 

 influence of sunlight and air. Another purpose 

 it fulfils is to convey the water absorbed by the 

 root-fibrils and root-hairs up to the leaves. In 

 some cases it has yet another office, that of stor- 

 ing up food-materials and water to supply the 

 necessities of the growing plant. The thick por- 

 tion of a radish or a beet, for example, though 

 usually called root, is not truly so named, as it 

 is in reality a development of the caulicle. The 

 direction of growth, the form, the absence of 

 root-hairs, branches, and, of course, of a root-cap, 

 all serve to distinguish the caulicle from the 

 radicle. 



The Primary Bud. — Above the two seed-leaves 

 we find the young growing leaves closely crowded 

 together and forming a "bud", such bud consist- 

 ing of a very short stem from the sides of which 

 are given off the leaves. This, the first bud of 

 a plant, is called the plumule. In the case of an 

 annual plant this plumule is the only real bud 

 that the plant makes; for the formation of a 

 bud, as we shall see later on, implies a check or 

 arrest of growth, which does not occur, at least 

 not in a very definite way, in the life of an 

 annual plant. In any case, whether the plant 

 live through one season or through many, the 

 "plumule", or first bud, gradually lengthens, 

 dilates, becomes succulent or hardens into wood, 

 remains unbranched, or, as is more usually the 



