THE ROOT THE STEM. 



A Bulbous Root is a root which, superadded to numerous 

 fibres, has an enlarged, more or less spherical part, or bud, 

 which may be solid (Fig. 6.) ; coated, composed of concentric 

 layers (Fig. 7.) ; or scaly, consisting of thick scales. (Fig. 8.) 



A Granulated Root (Fig. 9.) consists of numerous small 

 bulb-like buds or scales strung together. 



The duration of the root determines that of the plant. When 

 the root lasts only one year, the plant is said to be Annual. 

 When it continues two years, the plant is Biennial; when 

 more than two years, Perennial. 



OF THE STEM. 



The Stem is that part of the plant which, rising above ground, 

 supports the leaves and flowers. 



Some plants have no stem, or only a very short one, and are 

 therefore denominated stemless. 



Others have a soft stem, which, after the fruit is perfected, 

 decays, and is named herbaceous. 



Others again have a hard woody stem. Plants possessed of 

 this kind of stem are, when large, called Trees ; when small, 

 Shrubs. 



In the woody stem there are distinguished the following 

 parts : the cuticle or epidermis, the external thin filmy covering ; 

 the cellular integument, a thin layer under the epidermis ; the 

 outer bark, generally of a brown or gray colour ; the inner 

 bark, a whitish, soft, fibrous, and very flexible part, lying 

 under the outer bark ; the alburnum, or layers of young wood 

 next to the inner bark ; the duramen or hard wood, also in 

 layers ; and lastly, the pith, a white, cellular, spongy sub- 

 stance, occupying the centre of the stem, and enclosed by the 

 medullary sheath. 



The stems of trees and shrubs growing in our climate are all 

 of this kind. They increase in size by the addition of a new 

 layer of wood every year to the alburnum, and of a thinner 

 layer to the inner bark. It is thus between the wood and the 

 bark, that the substance is formed, which, at first a clammy 

 fluid, named Cambium, is, according to some, gradually or- 

 ganized, and converted into wood and bark. Plants that in- 

 crease in size in this manner, are called Exogenous, that is, 

 growing outwards, because their growth takes place near the 

 surface. But palms, and other trees of tropical countries, hav- 

 ing no distinction of parts into pith, woody layers, bark, and 

 B 



