92 THE STKM, 



characteristics of the stem. These are produced only at certain 

 definite and symmetrically arranged points, called 



156. Nodes, literally knots, so named because the tissues are here 

 more or less condensed, interlaced, or interrupted, as is conspicuous- 

 ly seen in the Bamboo, in a stalk of Indian Corn, or of any other 

 Grass. Here each node forms a complete ring, because the leaf 

 fcses from the whole circumference of the stem at that place. 

 When the base of the leaf or leafstalk occupies only a part of the 

 circumference, the nodes are not so distinctly marked, except by 

 the leaves they bear, or by the scars left by their fall (Fig. 151, &c.) 

 They are often called joints, and sometimes, indeed, the stem is 

 actually jointed, or articulated, at these points ; but commonly there 

 is no tendency to separate there. Each node bears either a single 

 leaf (as in Fig. Ill, 121, &c.), or two leaves placed on opposite 

 sides of the stem (as in Fig. 107), or else three or more, placed in 

 a ring (in botanical language, a whorl or verticil) around the stem. 

 The naked portions or spaces that intervene between the nodes are 

 termed 



157. luternodes. The undeveloped stem is, in fact, made up of a 

 certain number of these leaf-bearing points, separated by short in- 

 tervals ; and its growth consists, primarily, in the successive elonga- 

 tion of these internodes _so as to separate the nodes more or less, and 

 allow the leaves to expand. 



158. This brings to view the leading peculiarity of the stem ; 

 namely, that it is formed of a succession of similai- parts, developed 

 one upon the summit of another, each mth its own independent 

 growth. Each developing internode, moreover, lengthens through- 

 out its whole body, unlike the root, which elongates continuously 

 from its extremity alone (121). To have a good idea of this, we 

 have only to observe the gradual evolution of a germinating plant, 

 where each internode develops nearly to its full length, and ex- 

 pands the leaf or pair of leaves it bears, before the elongation of 

 the succeeding one commences. As already described (120, &c.), 

 the radicle, or internode which pre-exists in the embryo, elongates, 

 and raises the seed-leaves into the air ; they expand and elaborate 

 the material for the next joint, the leaves of which in turn prepare 

 the material for the third, and so on. The internode lengthens 

 principally by the elongation of its already formed cells, particularly 

 in its lower part, which continues to grow after the upper portion 

 has finished. 



