e. verted into the proper food of the plant. - 
ELEMENTS OF BOTANY. xi 
23. A Runner is a thread-like prostrate branch, producing roots and a tuft of 
leaves at its extremity. 
24. Spines, or Thorns, are imperfectly developed, leafless branches, with hard 
tips. 
25. Tendrils are the thread-like spirally coiled branches of weak and slender 
plants, by means of which they attach themselves to other and stronger objects 
for support. Leafstalks and parts of the inflorescence are occasionally convert- 
ed into tendrils. 
26. Plants which die down to the ground at the close of the season, or after 
maturing seed, are called Herbs, or Herbaceous Plants. Those with woody stems, 
lasting from year to year, when of humble size, are called Shrubs, and when 
reaching an elevation of twenty feet or more, Trees. 
4 Internal kivaitens of Stems. 
27. The stems of Phenogamous Plants are composed of cellular tissue, woy 
tissue, and vessels; and upon the arrangement of the latter are founded the two 
divisions of Kicopewur and Endogenous Plants. 
28. Exogenous stems consist of a central column, called the Pith; an EINE 
covering, called the Bark; and a middle portion, called the Wood. 
29. Their Pith is a mass of cellular tissue, enclosed in a thin sheath of spiral 
rre termed the Medullary Sheath. 
30. Their Wood is composed of one or more layers of woody and vascular 
tissue, traversed by thin plates of cellular tissue, called ry rays, and 
| MW called the ADurnum, or 
Sap-wood, and the ‘older and harder | porto, the Duramen, or Heart-wood. 
. 81. The Bark, like the wood, is made up of layers. The inner bark, or Lie, 
is composed chiefly of woody fibre. Between it and the wood, in the growing 
season, is secreted a thin mucilage, called the Cambium, in which the new layers 
of wood and bark are developed. Surrounding the inner bark is the Green bark, 
consisting of cellular tissue filled with Chlorophyll, or the green matter of veg- 
etables. Covering the whole is a thin membrane of cellular tissue, called the 
Epidermis, or Cuticle. 
32. Endogenous stems exhibit no distinction of pith, wood, and bark; but 
are composed of threads or bundles of woody tissue, irregularly embedded in 
cellular tissue. They increase in diameter by the formation of new bundles, 
which are chiefly directed to the centre of the stem. 
5. The Leaves. * 
33. bens are expanded appendages of the stem, arit from axillary 
and terminal buds. They consist of loose cellular tissue, supported by a net- 
work of woody and vascular tissue, called veins or ribs, and protected by the - 
epidermis. In them the fluids received from the root, and what they imbibe - 
from the air, through minute openings in the epidermis, called stomata, 
di de de bud, d are folded, hid, or cd in votos 
