THE BOOT. 



15 



Exceptions. The statement that roots descend is subject to a few ex- 

 ceptions in the cases of the lateral ramifications of roots, and of the lateral 

 roots formed by parasitical and by certain climbing plants, which often 

 retain their original direction, making a more or less obtuse angle with the 

 stem from which they rise. In some Cycads and Arads the root-branches 

 ascend vertically. These exceptions are less numerous than the deviation 

 of the stem from its general character as the ascending nart of the axis, since 

 in a large number of perennial plants the direction of the main stem is con- 

 stantly horizontal. Stems of this kind are of frequent occurrence among 

 perennial herbaceous plants, and are ordinarily termed by gardeners 

 "creeping roots:" for example, those of the Lily of the Valley (fig. 4), 

 Garden Flag, Couch Grass, *fcc. Roots, as a general rule, are destitute of 

 leaves and leaf-buds, which fact serves to distinguish them from rhizomes 

 or root-stocks (STEMS). But the distinctions between root and stem are 

 not absolute : many exceptional instances occur, and some transitional 

 ones ; thus, under certain circumstances, roots, as indeed every part of the 

 vegetable structure, may be made to form buds, but always from the 

 sides, never from the end as in stems. Some trees are especially prone to 

 this, and may be propagated by cuttings of the root, such as Pyrusjapo- 

 nica, Madura aurantiaca, the Plum-tree, &c. The root of Anemone 

 japonica likewise produces buds very readily. The roots of Neottia bear 

 leaves, while, on the other hand, some Orchids, as JEpipogon Gmelini and 

 Corallorhiza innata, and some Bromeliads have no roots. 



Origin of the Root. The true root of the embryo plant is the 

 downward continuation of the axis ; but -p. * 



the original radicle, the real inferior extre- 

 mity of the axis in the Monocotyledons and 

 in the stem-forming Flowerless plants (such 

 as the Ferns), in most cases speedily ceases 

 to grow, and the efficient roots are really 

 lateral organs. Where the primary radicle 

 is developed, we have a true root (fig. 5) ; 

 but the roots which are produced from the 

 sides of stems, or from leaves, are termed 

 adventitious roots (fig. 4). 



The axial root may be seen well in any seed- 

 ling Dicotyledonous plant, as in a young Bean 

 or Turnip ; and by watching the germination of 

 a few seeds of such plants, the development of 

 the radicle into the axial root may be readily 

 traced. The axial nature of the root is clearly- 

 evident in the full-grown plants of most annual 

 garden species of Dicotyledons ; and in shrubby 

 and arborescent perennials of this class the axial 

 root is persistent, growing by annual increase 

 into a large woody mass, proportionate to that 

 of the ascending stem or trunk. 



The origin of adventitious roots may be observed in germinating seeds 



Root of the Mallow (Malva 

 rotundifolia). 



