44 



THE STEM. 



have seen stems of this kind increase several times their ori- 

 ginal diameter. Generally they are nearly cylindrical and 

 the trees high, compared with their diameters, having their 

 foliage entirely at their summit. Perhaps no circumstance 

 strikes the beholder as more singular in a grove of these trees, 

 than the columnar appearance of the stems, and the rich fo- 

 liage of their tops, presenting an appearance of an immense 

 arbor supported by lofty columns. 



50. The second variety of Endogenous stems are such as 

 have nodes at certain intervals, and with fistular internodes, 

 ^r^ij^ as seen in fig. 17, which represents a transverse 

 section of the cane, and lig. 18, a lontjitudinal 

 section of a node of the same plant. 

 The cane is a good type of this va- 

 riety, which includes the grasses 

 and grains. If we examine a cane, 

 we find it composed of a thin, and an exceed- | 

 ingly hard, siliceous-like cuticle. It is general- 

 ly supposed, however, that the silex lies beneath 

 the cuticle, and does not forai a part of it. By 

 cutting into the stem, we find it composed of 

 cellular substance with fibres imbedded in it, the 1 

 fibres being more numerous, and the substance harder the 

 nearer it is to the circumference. That part of the cylinder 

 lying next the cavity consists almost entirely of cellular tis- 

 sue. The nodes are formed by the accumulation of cellular 

 substance between the fibres, and form a firm basis, forcing 

 them asunder, and filling up the cavity for the attachment of 

 leaves and branches, when circumstances induce their devel- 

 opment. The fibres of this variety of stems are not interla- 

 ced as in the preceding, as may be seen by the splitting of 

 the stem either into layers or strips. The leaves have their 

 origin only at the nodes, while every part of the stem in the 

 preceding variety becomes the origin of leaves. The nodes 

 have been considered by some Botanists as separating the 

 plant into as many distinct individuals as there were nodes ; 

 but there is no reason in our opinion for such a hypothesis, 

 since we may easily trace the fibres through the nodes, and 

 the nodes differ in no respect from any other part of the stem 

 excepting the accumulation and hardening of cellular sub- 

 stance, and this apparently for the purpose of forming a sit- 

 uation for the leaves. 



51. Tiie third variety are such as have solid stems, and 

 some of them with nodes, and others with branches. The 

 smilax affords a good example of the former variety, and it 

 approaches nearer in appearance, both by its stem and leaves, 



